31 Mar
2012
31 Mar
'12
1:20 a.m.
for the purpose of expunging the screen rot. Need to get behind the screen thingee there
12:04 p.m.
Dropping them from a high place usually does the trick ;-)
While this is probably a quicker way of gettign the casing off, the time
taken to put it back on again is much longer than with the 'remove the
screw' method. And I think it's the total repair time that's important.
-tony
11:12 p.m.
VR201? Remove screw under cover in the centre of the rear panel between
plug and pots. Lower adjustment leg to fully out.
Screen blue spot?
a) Run a hot wire (Styrofoam cutter) between the outer screen and the front
of the tube.
Or
b) (only for CRT familiar persons) Remove the tube completely. Place in
something to support it at the face end. Don goggles and gloves. Chip away
the outer faceplate bit by bit. Peel off the soft plastic. Polish up the
tube front, rebuild the monitor and put spacers at the four corners then
replace casing. Does wonders for the brightness as well.
Regards
?
Rod Smallwood
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 31 March 2012 20:05
To: cctalk at classiccmp.org
Subject: Re: how do you crack (open) a Rainbow mono monitor?
Dropping them from a high place usually does the trick ;-)
While this is probably a quicker way of gettign the casing off, the time
taken to put it back on again is much longer than with the 'remove the
screw' method. And I think it's the total repair time that's important.
-tony
1 Apr
1 Apr
9:54 a.m.
________________________________
From: Rod Smallwood <rodsmallwood at btconnect.com>
VR201?? Remove screw under cover in the centre of the rear panel between
plug and pots. Lower adjustment leg to fully out.
C: Thought I did that on the first try. It didn't seem easy to get the screws back in
(in fact I gave up). I'll give it another go.
2 Apr
2 Apr
11:46 a.m.
Remove screw under cover in the cen=
tre of the rear panel between=0Aplug and pots. Lower adjustment leg to full=
y out. =0A=0AC: Thought I did that on the first try. It didn't seem easy to=
get the screws back in (in fact I gave up). I'll give it another go.=0A
I am puzzled as ot the reference to 'screws'. I think there's only one
screw, a relatively large Phillips head one onder the plastic dome cover
on the back. Are you removing soemthign else?
-tony
1 Apr
1 Apr
1:16 p.m.
VR201? Remove screw under cover in the centre of the rear panel between
plug and pots. Lower adjustment leg to fully out.=20
Screen blue spot?=20
a) Run a hot wire (Styrofoam cutter) between the outer screen and the fro=
nt
of the tube.
Or =20
b) (only for CRT familiar persons) Remove the tube completely. Place in
something to support it at the face end. Don goggles and gloves. Chip awa=
y
the outer faceplate bit by bit. Peel off the soft plastic. Polish up the
tube front, rebuild the monitor and put spacers at the four corners then
replace casing. Does wonders for the brightness as well.
Look, I know what day it is, but practical jokes are supposed to be
funny, and not endager innocent bystnaders at som random future time.
CRT implosions are not common, I agree. But they must be serious enough
tat even in the less safety-concious times of 50 years ago all TV sets
had some kind of implosion protection.
Unless you have definiete infroamtion to the contrary, I will go by what
every CRT data sheet I've looked at says. That the twin-panel faceplate
acts like a laminated windscreen and supports te screen i nthe even of an
implosion, preventing the user from being showeed in fragments of glass.
Most CRT datasheets also say that no attempy must be made to remvoe the
outer layer, but I think it's popsible to do this safely _provided you
then re-bond the layers together properly_. LEaving off the outer layer,
or not bonding it to the frotn of the envelope is not acceptable IMHO.
You don't know when the CRT could implode, or who might be in front of it
at the time.
-tony
10:50 p.m.
Whilst I do agree your safety concerns. I would say not all tubes have this
arrangement and that the thin bits are at the other end. The point is the
tube is being supported as intended at the four front corners by the metal
band made for that purpose.
Having spent some time in a re-gunning facility maybe I'm just used to CRT's
Regards
?
Rod Smallwood
?
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 01 April 2012 21:16
To: cctalk at classiccmp.org
Subject: Re: how do you crack (open) a Rainbow mono monitor?
VR201? Remove screw under cover in the centre of the rear panel between
plug and pots. Lower adjustment leg to fully out.=20
Screen blue spot?=20
a) Run a hot wire (Styrofoam cutter) between the outer screen and the fro=
nt
of the tube.
Or =20
b) (only for CRT familiar persons) Remove the tube completely. Place in
something to support it at the face end. Don goggles and gloves. Chip awa=
y
the outer faceplate bit by bit. Peel off the soft plastic. Polish up the
tube front, rebuild the monitor and put spacers at the four corners then
replace casing. Does wonders for the brightness as well.
Look, I know what day it is, but practical jokes are supposed to be
funny, and not endager innocent bystnaders at som random future time.
CRT implosions are not common, I agree. But they must be serious enough
tat even in the less safety-concious times of 50 years ago all TV sets
had some kind of implosion protection.
Unless you have definiete infroamtion to the contrary, I will go by what
every CRT data sheet I've looked at says. That the twin-panel faceplate
acts like a laminated windscreen and supports te screen i nthe even of an
implosion, preventing the user from being showeed in fragments of glass.
Most CRT datasheets also say that no attempy must be made to remvoe the
outer layer, but I think it's popsible to do this safely _provided you
then re-bond the layers together properly_. LEaving off the outer layer,
or not bonding it to the frotn of the envelope is not acceptable IMHO.
You don't know when the CRT could implode, or who might be in front of it
at the time.
-tony
2 Apr
2 Apr
12:15 p.m.
Whilst I do agree your safety concerns. I would say not all tubes have th=
is
arrangement and that the thin bits are at the other end. The point is the
tube is being supported as intended at the four front corners by the meta=
l
band made for that purpose.
I am sure the tension band is also part of the implosion protection, and
you are leaving that alone. However, I've seen CRT data sheets which stat
that the CRT has a 'twin panel faceplate' or soemthing similar and that
this is also part of the implosion protection system.
My view is that unless you _know_ the CRT can't implode violently even
with the outer faceplate removed, you should not leave it off.
Unfortunately, no manufacture is going to say that (even if it is true),
due to liabiltiy concerns, so I don't know how to be sure.
Having spent some time in a re-gunning facility maybe I'm just used to CR=
T's
I am not commmenting on the fact that yuou're doing things that could be
dangerous if doen incorrectly _while you are doing them_. Let me give you
an analogy. I think we all agree that 400V DC at essentially unlimited
current is lethal. And yet many of us routinely work on SMPUs that have
that sort of voltage derrived directly from the mains. I try to be
careful when I;m working on one...
But, no way would I leave a device in service with the 400V rail exposed.
It's one thing to have it l;ike that on the bench when you're the only
person around, it's quite another when other people might ocme into
contact with it. I would not have a machine 'in use' with safety covers
on the PSU remvoed or missing.
And IMHO it's the same with CRTs. If you know what yo are doing, it is
almost certainly safe to cut trhoug hthe bonding, remvoe he faceplate and
rebond it. But I feel you should end up wit hthe CRT in as safe a
condition as it was when it was made. Not with protecive parts remvoed.
-tony
2:13 p.m.
New subject: how do you crack (open) a Rainbow mono monitor? (LEVITY?, APRIL FOOLS? Please clarify.)
if there is any postings in this thread which could later be found by
someone unfamiliar with CRT's and they were posted in jest, can someone
tag those threads and postings?
this is way to serious a subject to have joke material in for someone to
discover in a couple of years and blow up a CRT of any sort.
Like joking about observing solar eclipse events on a serious astronomy
thread in the obvious ways.
Just saying. I am still not sure from what I saw if anyone was joking
around, with things like the hot wire treatment,etc, but I'd never post
that as any approach unless one had their life insurance paid up.
I'm posting on replies by tony, who is serious and am not referring to
him except that he was the latest to express confusion about whether the
info and query was serious or a joke.
Apologies if it was serious, but I'm not clear seeing this, and it is
not particularly a joking matter.
3 Apr
3 Apr
12:36 p.m.
New subject: how do you crack (open) a Rainbow mono monitor? (LEVITY?, APRIL
if there is any postings in this thread which could later be found by
someone unfamiliar with CRT's and they were posted in jest, can someone
tag those threads and postings?
this is way to serious a subject to have joke material in for someone to
discover in a couple of years and blow up a CRT of any sort.
I love a practical joke, I have played quite a few in my time, and I have
had plenty played aginst me (if you're going to 'give' you have to
'take' as well).
But a practical joke has to be funny for all conceened in the end. The
victim may moan at the time, but will end up laughing I hope. If only
laughing at himself.
For that reason, I do not regard anything that could cause loss or damage
to the victims property (the perpetrator's property is another matter
:-)), injury or death to be a practical joke. Period. And therefore I
will necer jest (not even on 1st April) about things that could be
dangerous, like CRTs or high voltages, or that could cause serious damage
or loss of data.
Of course I can make mistakes in my postings, and I cannont be held
legally responsible for anything that happens if you follow my advice.
But I can assure you it's all 'in good faith'.
There was a jest, cleaerly recognised as such, in at least one service
manual years ago. When it came to fitting the yoke to the CRT, the
instructions were soemthing like 'Tighten the clamp until the CRT
implodes, then back of 1/4 of a turn' :-).
Like joking about observing solar eclipse events on a
serious astronomy
thread in the obvious ways.
Just saying. I am still not sure from what I saw if anyone was joking
around, with things like the hot wire treatment,etc, but I'd never post
that as any approach unless one had their life insurance paid up.
There are 2 issuee here, IMHO. One is the dgner to the person doign the
repair, the other is the danger to possible future uses of the monitor if
the CRT implosion protection is not adequate.
It is perfectly possible to use a hot (not very hot, certainly not
glowing) wire to cut the adhesive between the 2 layers of the faceplate.
It's moderately hazardous, no worse than anything else many of us do. I
would not want to do it without googles or better a face shield. nd
perhaps the advice in the MG1 technical manual of a 'heavy cnvas apron to
proect those other precious parts' is a good idea too.
This is very much something you should only attmept if you know what you
are doing.It's like working with the mains or using machine tools. Plenty
of people do those things and live to tell the tale. Equally, a mistake
can be fatal, so you need to know what you are doing and take care.
Personally, I'd still want to rebond the faceplate to the CRT, even
though, given the tension band, it's probably OK without it. That's an
issue of safety to future users. A CRT imploding is not fun, I can assure
you.
-tony
2:07 p.m.
New subject: how do you crack (open) a Rainbow mono monitor? (LEVITY?, APRIL
There was a jest, cleaerly recognised as such, in at
least one
service manual years ago. When it came to fitting the yoke to the
CRT, the instructions were soemthing like 'Tighten the clamp until
the CRT implodes, then back of 1/4 of a turn' :-).
Heh. I suppose you could take it as a filter: if you take that
instruction seriously, you have no business even taking the cover off
the unit. (Unfortunately there's no way to make it actually prevent
you from....)
This is very much something you should only attmept if
you know what
you are doing.
My father used to test lightbulb sockets for liveness by sticking his
finger in them to see if he got a tingle between base and side.
It is possible to do this safely. It is also possible to kill yourself
attempting it. So I would never recommend it; anyone who understands
electricity enough to do it safely doesn't need the recommendation, and
anyone who doesn't is better off without it.
/~\ The ASCII Mouse
\ / Ribbon Campaign
X Against HTML mouse at rodents-montreal.org
/ \ Email! 7D C8 61 52 5D E7 2D 39 4E F1 31 3E E8 B3 27 4B
4 Apr
4 Apr
10:58 a.m.
New subject: how do you crack (open) a Rainbow mono monitor? (LEVITY?, APRIL
There was a jest, cleaerly recognised as such, in
at least one
service manual years ago. When it came to fitting the yoke to the
CRT, the instructions were soemthing like 'Tighten the clamp until
the CRT implodes, then back of 1/4 of a turn' :-).
Heh. I suppose you could take it as a filter: if you take that
instruction seriously, you have no business even taking the cover off the unit. (Unfortunately there's no way to make
it actually prevent
you from....)
Thankfully... The last think I (or anyone else here) needs are
manufacturers thginking they should eb able to stop us repairing things.
A lot of the repairs I, and others, do are certainly not going to be
approved by the origianl manufacturer (they're not dangerous, or
unrelaible, I might add...)
This is very much something you should only
attmept if you know what
you are doing.
My father used to test lightbulb sockets for liveness by sticking his
finger in them to see if he got a tingle between base and side.
It is possible to do this safely. It is also possible to kill yourself
attempting it. So I would never recommend it; anyone who understands
electricity enough to do it safely doesn't need the recommendation, and
anyone who doesn't is better off without it.
Agreed. People who have been 'in the game' for some time know safe ways
to do thigns that could be lethal if done wronging. It is a bad idea to
teach such tricks IMHO, you have to discover them for yourself. Only that
way will you know how ot do them safely under all conditions, becuase you
really understnad what you are doing.
-tony
3 Apr
3 Apr
6:07 a.m.
All well and good. One tiny point. I worked for DEC Terminals Product Line
when those items where in current production.
The tubes were just fine without the face plate and met all implosion
requirements. Some (Green I think) did not have them at all.
However certain national safety specifications required the second screen
and its anti splinter layer. This was regardless of if the underlying tube
met the implosion spec. The spec was that it was present and its materials
met the requirements.
I think they put them on all the white ones to save having two different
cases.
I am perhaps a bit over familiar with the way I handle CRT's. However in the
time when I was a student apprentice in the 1960's I did work in a High
Voltage test lab (Anybody for a bit of 500KV?) and the guy I worked for had
been part of the original EMI television development team in the late 1930'.
Guess who got stuck with mending cranky 1950's TV's with live chassis?
"Isolation Transformer Rod? What do you want one of those for?"
I passed all of the safety tests. In those days they consisted of still
being alive when you left.
Regards
?
Rod Smallwood
?
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 02 April 2012 20:16
To: cctalk at classiccmp.org
Subject: Re: how do you crack (open) a Rainbow mono monitor?
Whilst I do agree your safety concerns. I would say not all tubes have th=
is
arrangement and that the thin bits are at the other end. The point is the
tube is being supported as intended at the four front corners by the meta=
l
band made for that purpose.
I am sure the tension band is also part of the implosion protection, and
you are leaving that alone. However, I've seen CRT data sheets which stat
that the CRT has a 'twin panel faceplate' or soemthing similar and that
this is also part of the implosion protection system.
My view is that unless you _know_ the CRT can't implode violently even
with the outer faceplate removed, you should not leave it off.
Unfortunately, no manufacture is going to say that (even if it is true),
due to liabiltiy concerns, so I don't know how to be sure.
Having spent some time in a re-gunning facility maybe I'm just used to CR=
T's
I am not commmenting on the fact that yuou're doing things that could be
dangerous if doen incorrectly _while you are doing them_. Let me give you
an analogy. I think we all agree that 400V DC at essentially unlimited
current is lethal. And yet many of us routinely work on SMPUs that have
that sort of voltage derrived directly from the mains. I try to be
careful when I;m working on one...
But, no way would I leave a device in service with the 400V rail exposed.
It's one thing to have it l;ike that on the bench when you're the only
person around, it's quite another when other people might ocme into
contact with it. I would not have a machine 'in use' with safety covers
on the PSU remvoed or missing.
And IMHO it's the same with CRTs. If you know what yo are doing, it is
almost certainly safe to cut trhoug hthe bonding, remvoe he faceplate and
rebond it. But I feel you should end up wit hthe CRT in as safe a
condition as it was when it was made. Not with protecive parts remvoed.
-tony
1:07 p.m.
All well and good. One tiny point. I worked for DEC Terminals Product Lin=
e
when those items where in current production.=20
I could counter that by saying that while you may well hvee designed
things that used said CRT, and may have handled the CRTs for many years,
this does not mean you know exactly how the CRTs themselves were
designed, and whether they remain sade if you remvoe the front glass layer
I don't beelvie DEC designed the CRT, they bought it in. I am nto even
sure all came from one manufacturer, in which case it may well be that
some CRRTs are safe without the outer glass, some are not. _I_ don't
know, and I'd rather not be showered in glass fagments to find out.
The tubes were just fine without the face plate and
met all implosion
requirements. Some (Green I think) did not have them at all.=20
Interesting. I am suprised there are any differentces between the CRt
other than the phosphor. Why was this? Did all colours of CRT come from
the same manufacturer?
It probably is safe to run the CRT without the outer glass sheet, and I am
sure you know what you are doing.
However certain national safety specifications required the second screen
and its anti splinter layer. This was regardless of if the underlying tub=
e
Now tha I can well believe :-). My experience of safety requirements is
that there are often hoops you have to jump through for no good reason.
How did the green CRTs get roudn this (or were monitors/terminals fitted
with said CRTs simply not sold in such countries?
met the implosion spec. The spec was that it was
present and its material=
s
met the requirements.=20
I think they put them on all the white ones to save having two different
cases.
I am perhaps a bit over familiar with the way I handle CRT's. However in =
I am perhaps too far the other way. My father spend much of his working
life working with UHV systems (and to be fair, the forces on the
envelopedon't really change that much as the vaccum gets harder...) and
had a few things implode. He warned me to take great care...
the
time when I was a student apprentice in the 1960's I did work in a High
Voltage test lab (Anybody for a bit of 500KV?) and the guy I worked for h=
ad
been part of the original EMI television development team in the late 193=
0'.
Guess who got stuck with mending cranky 1950's TV's with live chassis?
Been there, done that... It wasn't so bad on the valve sets with half
wave rectificions, with a bit of care you could ensuee the chassis was
connected to the neutral side of the mains [1] and thus be relatively
safe. The later IC-based sets with bridge rectifiers were worse,
whichever way round the plug was connected, the chassis was live.
[1] A common way to do this was to use one of those neon tester
screwdrivers which would light up if touched on a live chassis. If so,
revese the mains conenctions. A _NOT FUNNY_ 'joke' was to convice the
newbie that if he took his screwdriver apart and turned the neon round,
it would then light on a dead chassis. (Of course it does no such thing,
it still lights on a live one).
"Isolation Transformer Rod? What do you want one
of those for?"
The serivec information for the PSU in one of my Philips machines
includes all the waveforms round the chopper circuit. This is a SMPSU
with a mains bridge rectifier. The instructions for obvserving these
waveforms tell you to use an isolating transformer, or if this is not
available to disconenct the maisn warth wirew in the 'scope mains plug.
Err, i have this slight objection to a 'scope with a live cabinet :-)
I passed all of the safety tests. In those days they consisted of still
being alive when you left.
Seems reasoanble :-)
-tony
1:51 p.m.
More importantly, how do you turn a Dec Rainbow monitor into a crack pipe?
But I digress... I found a HP colorpro plotter at work today,
gathering a thick layer of dust.
Anyone know how to make it go?
--
Yoyodyne Propulsion Systems: ?"The Future Begins Tomorrow"
Visit us at: http://www.yoyodyne-propulsion.net
--------
They view life as a bunch o' unconnected incidents 'n things. They
don't realize that there's this, like, lattice o' coincidence that
lays on top o' everything. Give you an example; show you what I mean:
suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll
say, like, plate, or shrimp, or plate o' shrimp out of the blue, no
explanation. No point in lookin' for one, either. It's all part of a
cosmic unconciousness.
-Miller, Repo Man
4 Apr
4 Apr
1:40 a.m.
On Wed, Apr 4, 2012 at 1:43 AM, Chuck Guzis <cclist at sydex.com> wrote:
On 3 Apr 2012 at 17:14, Eric Smith wrote:
Well, there is a skateboard park around here. . . I don't think even
several model rocket engines would lift it. If I still lived in
Arizona, a shotgun might be appropriate. Thanks for the advice!
--
Yoyodyne Propulsion Systems: ?"The Future Begins Tomorrow"
Visit us at: http://www.yoyodyne-propulsion.net
--------
They view life as a bunch o' unconnected incidents 'n things. They
don't realize that there's this, like, lattice o' coincidence that
lays on top o' everything. Give you an example; show you what I mean:
suppose you're thinkin' about a plate o' shrimp. Suddenly someone'll
say, like, plate, or shrimp, or plate o' shrimp out of the blue, no
explanation. No point in lookin' for one, either. It's all part of a
cosmic unconciousness.
-Miller, Repo Man
Strap a rocket to it?
Well, you're more ambitious than I. ?I was going to suggest strapping
it to a skateboard and releasing it at a skateboard park.
Shows my lack of imagination. 
12:59 p.m.
John Many Jars wrote:
I don't think even several model rocket engines
would lift it.
Who said anything about "model" rocket engines? :-)
On a more serious note, it used to be that Windows actually had drivers
for HPGL plotters. I haven't checked in a long time, but I doubt that
recent versions of Windows still have that. I'd expect that some CAD
packages can probably still speak HPGL.
1:09 p.m.
On 04/04/2012 03:59 PM, Eric Smith wrote:
On a more serious note, it used to be that Windows
actually had drivers
for HPGL plotters. I haven't checked in a long time, but I doubt that
recent versions of Windows still have that. I'd expect that some CAD
packages can probably still speak HPGL.
They do. The whole architectural industry is still based on HPGL,
with no particular reason to change.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
1:17 p.m.
On 04/04/2012 20:59, Eric Smith wrote:
(are you the Eric that worked at Cern and ranted about VI?)
John Many Jars wrote:
Windows no longer has HPGL drivers. You can get Roland HPGL drivers that
work up to XP with most HPGL plotters. I use them with my HP and HPDS
plotters. There are third part plotter drivers that will work with many
HPGL plotters available from :-
http://www.winline.com/evalpen.html
but the real one is very expensive. As you surmise many packages can
still be persuaded to produce HPGL. I also wrote a mod to (aka hacked)
the IBM 1130 SIMH package so it would plot HPGL. You can see it driving
my Hitachi plotter here:-
http://www.youtube.com/watch?v=SCUUgLvVvpg
Dave
G4UGM
I don't think even several model rocket
engines would lift it.
Who said anything about "model" rocket engines? :-)
On a more serious note, it used to be that Windows actually had
drivers for HPGL plotters. I haven't checked in a long time, but I
doubt that recent versions of Windows still have that. I'd expect
that some CAD packages can probably still speak HPGL.
10:53 a.m.
More importantly, how do you turn a Dec Rainbow monitor into a crack pipe=
?
With a glassblowing torch?
But I digress... I found a HP colorpro plotter at work today,
gathering a thick layer of dust.
Anyone know how to make it go?
Is this an HP7440? What interface does it have (I think both RS232 and
HPIB models were made)? You can probably find manuals to download at
http://www.hpmuseum.net/ those should tell you the command set (which
is, not suprisingly, HPGL) and how to configure it.
-tony
3 Apr
3 Apr
3:26 p.m.
On 04/03/2012 04:07 PM, Tony Duell wrote:
Your belief is not a factor, you didn't work for DEC.
Rod and I both worked for DEC, I also worked with the terminals people
during the Vt220, VT24x and VT320 series. DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
I'm old enough to rember and worked on old tVs that didn't have such
a safety layer. It was never an issue. For sport my brothers would
take the
tubes (CRT) from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. I've observed they
can be quite robust fromt he front but quite fragile from the neck side.
It had to do with acceleration voltages and part since the added glass was
leaded to meet EU/TUV standards for X-ray radiation.
Since DEC shipped to the major 13 markets they had to meet all their
standards. Not all made sense to us here in the USA but you do this to
sell things.
Some countries mandated specific eronomics and therefore allowable
colors, brightness, contrast and many more things. Often a cable that
was
correct in 10 of the 13 majors was disallowed because of the cordage
or colors used didn't meet the local rule. Ignoring the wall mains
connector
the cable itself was a often 13 differnt cords because of internal
construction.
So cables it was easy to be destination specific but for a thing that was
used/manufacured in great quantity the standardized design was the rule.
DEC even had internal standard for designing for international sale and
it required all products (with exceptions) to meet internationalization
requirements.
Still dangerous as the mains line can still be intercepted. You do
learn to behave well
to live long.
Back inthe day things were not always safe or smart, then again the people
working with it often were smarter. However, libility being what it is and
various govenments decreeing safety standards allowed both stupider
people to survive and to protect the unwary.
I alwas felt that anything mains powered without isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Allison
All well and
good. One tiny point. I worked for DEC Terminals Product Lin=
e
when those items where in current production.=20
I could counter that by saying that while you may well hvee(SP?) designed
things that used said CRT, and may have handled the CRTs for many years,
this does not mean you know exactly how the CRTs themselves were
designed, and whether they remain sade(SP?) if you remvoe(SP?) the front glass layer
I don't beelvie DEC designed the CRT, they bought it in. I am nto(SP?) even
sure all came from one manufacturer, in which case it may well be that
some CRRTs(SP?) are safe without the outer glass, some are not. _I_ don't
know, and I'd rather not be showered in glass fagments to find out.
The tubes were
just fine without the face plate and met all implosion
requirements. Some (Green I think) did not have them at all.=20
Interesting. I am
suprised there are any differentces(SP?) between the CRt(case)
other than the phosphor. Why was this? Did all colours of CRT come from
the same manufacturer?
It probably is safe to run the CRT without the outer glass sheet, and I am
sure you know what you are doing.
However
certain national safety specifications required the second screen
and its anti splinter layer. This was regardless of if the underlying tub=
e
Now tha I can well believe :-). My experience of safety requirements is
that there are often hoops you have to jump through for no good reason.
How did the green CRTs get roudn this (or were monitors/terminals fitted
with said CRTs simply not sold in such countries?
met the
implosion spec. The spec was that it was present and its material=
s
met the requirements.=20
I think they put them on all the white ones to save having two different
cases.
I am perhaps a bit over familiar with the way I handle CRT's. However in =
I
am perhaps too far the other way. My father spend much of his working
life working with UHV systems (and to be fair, the forces on the
envelopedon't really change that much as the vaccum gets harder...) and
had a few things implode. He warned me to take great care...
the
time when I was a student apprentice in the 1960's I did work in a High
Voltage test lab (Anybody for a bit of 500KV?) and the guy I worked for h=
ad
been part of the original EMI television development team in the late 193=
0'.
Guess who got stuck with mending cranky 1950's TV's with live chassis?
Been there, done that... It wasn't so bad on the valve sets with half
wave rectificions, with a bit of care you could ensuee(SP?) the chassis was
connected to the neutral side of the mains [1] and thus be relatively
safe. The later IC-based sets with bridge rectifiers were worse,
whichever way round the plug was connected, the chassis was live.
[1] A common way to do this was to use one of those neon tester
screwdrivers which would light up if touched on a live chassis. If so,
revese the mains conenctions. A _NOT FUNNY_ 'joke' was to convice the
newbie that if he took his screwdriver apart and turned the neon round,
it would then light on a dead chassis. (Of course it does no such thing,
it still lights on a live one).
"Isolation Transformer Rod? What do you want one of those for?"
The
serivec(SP?) information for the PSU in one of my Philips machines
includes all the waveforms round the chopper circuit. This is a SMPSU
with a mains bridge rectifier. The instructions for obvserving these
waveforms tell you to use an isolating transformer, or if this is not
available to disconenct(SP?) the maisn(SP?) warth(SP?) wirew(SP?) in the 'scope mains
plug.
Err, i have this slight objection to a 'scope with a live cabinet :-) 
3:39 p.m.
On 4/3/2012 4:26 PM, allison wrote:
I alwas felt that anything mains powered without
isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Come to think of I never have repaired a Component, I just buy a new
one and solder it in.
Allison
Ben.
3:48 p.m.
On 4/3/2012 4:26 PM, allison wrote:
Gasp! You've never ground the top off a dead DS1287 TOY clock chip to
replace
the failed lithium cell??
They were the famous CMOS clock/ram chips with the 10+year life tha usually
failed around years 4 to 6 and were unobtainium due to the high failure
rates
depleteing stocks.
That suggests a sheltered life! ;)
Allison
I alwas felt that anything mains powered without
isolation was
designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Come to think of I never have repaired a Component, I just buy a new
one and solder it in.
Allison
Ben.
4 p.m.
On 4/3/2012 4:48 PM, allison wrote:
They were the famous CMOS clock/ram chips with the
10+year life tha usually
failed around years 4 to 6 and were unobtainium due to the high failure
rates
depleteing stocks.
That suggests a sheltered life! ;)
No, I never had a computer last more than 4 to 5 years.
Allison
Ben.
4:30 p.m.
On 4/3/2012 4:48 PM, allison wrote:
All my classic gear is older than that! Some even have that &*(! chip.
They were most common in PCs more than 12 years ago.
Allison
They were the famous CMOS clock/ram chips with
the 10+year life tha
usually
failed around years 4 to 6 and were unobtainium due to the high failure
rates
depleteing stocks.
That suggests a sheltered life! ;)
No, I never had a computer last more than 4 to 5 years.
4:31 p.m.
On 04/03/2012 07:00 PM, ben wrote:
Wow. PCs I assume? I'd never put up with that crap. I want an
in-box upgrade path and some longevity.
-Dave
--
Dave McGuire, AK4HZ
New Kensington, PA
They were the
famous CMOS clock/ram chips with the 10+year life tha
usually
failed around years 4 to 6 and were unobtainium due to the high failure
rates
depleteing stocks.
That suggests a sheltered life! ;)
No, I never had a computer last more than 4 to 5 years.
1:12 p.m.
On 4/4/2012 12:32 PM, Tony Duell wrote:
I'm over 40 and still operational, that is the *important* thing.
No, I never had a computer last more than 4 to 5 years.
Hang on, this _is_ classiccmp, isn't it???
I've got machines that are over 40 years old still operational. -tony
In some cases lack of space has kept me from keeping classic
computer items, rather than them going *ka-boom*.
Ben.
PS. Now if I could get all the space taken with this modern PC
back, I'd have room for a *good* turntable and pre-amp.
5 Apr
5 Apr
11:09 a.m.
No, I never had a computer last more than 4 to 5
years.
Hang on, this _is_ classiccmp, isn't it???
I've got machines that are over 40 years old still operational. PS. Now if I could get all the space taken with this
modern PC
back, I'd have room for a *good* turntable and pre-amp.
Hmm.. A turntable on plinth is about 2' by 18" I think. The pre-amp,
well, it's only going to be 4 valves and no big rransformers, so that's
quite small.. You must be even shorter of space than I.
I was thinking that perhaps you meant an EMG accoustic gramophone with a
4' horn or similar, but then I notices the 'pre-amp'...
-tony
12:18 p.m.
As am I. I don't think I own any computers tht are
older than I am, alas.
My (several models of) KIM-1 is nearly as old as I am. It is the oldest
computer model in my collection. But I'm a young whippersnapper and I don't
mind people on my lawn, as long as they are attractive and female.
--
------------------------------------ personal: http://www.cameronkaiser.com/ --
Cameron Kaiser * Floodgap Systems * www.floodgap.com * ckaiser at floodgap.com
-- Arguments with furniture are rarely productive. -- Kehlog Albran -----------
2:59 p.m.
On 5 Apr 2012, at 12:18 PM, Cameron Kaiser wrote:
In my experience the exception you note does not change with advancing age. Thankfully.
--
Dr. Christian Kennedy
chris at mainecoon.com AF6AP
http://www.mainecoon.com PGP KeyID 108DAB97
PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97
"Mr. McKittrick, after careful consideration..."
As am I. I
don't think I own any computers tht are older than I am, alas.
My (several models of) KIM-1 is nearly as old as I am. It is the oldest
computer model in my collection. But I'm a young whippersnapper and I don't
mind people on my lawn, as long as they are attractive and female.
2:41 p.m.
New subject: mad music
On 4/5/2012 12:09 PM, Tony Duell wrote:
I was thinking that perhaps you meant an EMG accoustic
gramophone with a
4' horn or similar, but then I notices the 'pre-amp'...
I have this Easter Lilly with horn shaped flowers...now how to get
the sound into the plant from a 78?
-tony
Ben.
6 Apr
6 Apr
11 a.m.
New subject: mad music
On 4/5/2012 12:09 PM, Tony Duell wrote:
I have this mad vision of a plant-based reproduction system. You know, a
rose thorn as the stylus, a piece of flower petal as the diaphragm,
hollowed out bambooo as the interconnecting tubes, and a horn made of
fern leaves or soemthing...
Probably best enjoyed while inhaling the combusion prodcuts of certain
other plants...
-tony
I was thinking that perhaps you meant an EMG
accoustic gramophone with a
4' horn or similar, but then I notices the 'pre-amp'...
I have this Easter Lilly with horn shaped flowers...now how to get
the sound into the plant from a 78? 
4 Apr
4 Apr
12:24 p.m.
On Tue, Apr 3, 2012 at 6:48 PM, allison <ajp166 at verizon.net> wrote:
Gasp! ?You've never ground the top off a dead
DS1287 TOY clock chip to
replace the failed lithium cell??
I have done that (and on a Mostek MKT02 too). I've also replaced the
DS1287 with a DS12887. That works if the BIOS can handle it (not
guaranteed).
-ethan
11:30 a.m.
On 4/3/2012 4:26 PM, allison wrote:
That depends on the defintion of 'component'. If it's what's commonly
called a 'FRU', then I've certainly reparied them...
I've also repaired what are more often classed as components. Rewound
motors, inductors, transformers, rtc. Repaired switch contacts and
operating mechansisms. Rebuilt varaible capacitors. Even once repaired a
light bulb.
-tony
I alwas felt that anything mains powered without
isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Come to think of I never have repaired a Component, I just buy a new
one and solder it in.
11:28 a.m.
On 04/03/2012 04:07 PM, Tony Duell wrote:
Your belief is not a factor, you didn't work for DEC.
What the heck has that got to do with anything...
I stopped accepting the 'This is right because I say so' sort of arguemtn
when I was abotu 3 years old, and I have no intention of acceting it now.
It's very likely you and Ron are right, but, to quote the text over the
doorway of Kirkaldy's works in Southwark : 'Facts, not Opinions'.
All well
and good. One tiny point. I worked for DEC Terminals Product Lin=
e
when those items where in current production.=20
I could counter that by saying that while you may well hvee(SP?) designed
things that used said CRT, and may have handled the CRTs for many years,
this does not mean you know exactly how the CRTs themselves were
designed, and whether they remain sade(SP?) if you remvoe(SP?) the front glass layer
I don't beelvie DEC designed the CRT, they bought it in. I am nto(SP?) even
sure all came from one manufacturer, in which case it may well be that
some CRRTs(SP?) are safe without the outer glass, some are not. _I_ don't
know, and I'd rather not be showered in glass fagments to find out.
Rod and I both worked for DEC, I also worked with the
terminals people
during the Vt220, VT24x and VT320 series. DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
I am scpetical. If only because the CRTs in every DEC terminal I've been
inside has been a standard part with a normal type number.
Also, no manufacturer uses custom parts if they can avoid it. An
of-the-shelf part is cheaper and supply is more certain. And there is
absolutelly nothign odd about the dispaly circuitry in any VT series
terminal, or the performance requireds (resolution, etc) to require a
custom-made CRT
It's very likely DEC talked ot the CRT manufacturers, of course. But
mainly yo determine whcih CRT(s) would be suitable.
Anotehr thing, even if the CRT was custom-designed, I doubt very much the
requirment would have included 'Must be implosion-saft if soem hacker
removes the outer glass layer'. It would me much more likely to state
something like 'The CRT must have integral implosion protection to
<standard>) and the manufactuer decides how to comply with that. Given
that, any modication to the CRT could invalidate it.
I'm old enough to rember and worked on old tVs
that didn't have such
a safety layer. It was never an issue. For sport my brothers would
As am I...
FWIW, though, no TV set sold to the public in the UK ever had a CRT
pointing at the viewer without some kind of implosion protection. The
earlists sets (pre-wr) mounted the CRT vertically wit hthe screen on top,
the picture was viewed in a mirror. If the CRT imploded, the gass spreyed
upwards.
Later sets with the CRT conventionally mounted had a laminated glas or
(later) perspex sheild in front of the CRT. THen came tension bands and
laminated faceplate CRTs. Now, safety was takne a lot less seriously back
then, but they thougt this was enough of a danger for it to be necessary
to do something about it. And CRT implosion was, and is, not common.
take the
tubes (CRT) from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. I've observed they
can be quite robust fromt he (SPELL!) front but quite fragile from the
neck side.
Sure, the scree nad flare are thick glass, they have to be to withstand
atmospheric pressure. It's darn hard to break them.
But that is not the point. We are not only worried about somebody hitting
the screen. The other daner is stresses in the glasss causing it to
fracture spontaneously. And that does happen (I have met a TV engineer
who had a CRT crack across the screen one day for no apparent reason).
That's the big problem it can happen without warning.
The tubes
were just fine without the face plate and met all implosion
requirements. Some (Green I think) did not have them at all.=20
Interesting. I am
suprised there are any differentces(SP?) between the CRt(case)
other than the phosphor. Why was this? Did all colours of CRT come from
the same manufacturer?
It probably is safe to run the CRT without the outer glass sheet, and I am
sure you know what you are doing.
[1] A common
way to do this was to use one of those neon tester
screwdrivers which would light up if touched on a live chassis. If so,
revese the mains conenctions. A _NOT FUNNY_ 'joke' was to convice the
newbie that if he took his screwdriver apart and turned the neon round,
it would then light on a dead chassis. (Of course it does no such thing,
it still lights on a live one).
Still dangerous as the mains line can still be intercepted. You do
learn to behave well
to live long. I alwas felt that anything mains powered without
isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Hmmm.. Although at least over here j-random-public would pull off the back
and swap valves...
To be honest, I don't mucu care for non-isolated TVs and radios. I much
prefer a nice mains transformer and parallel heaters. But I can see the
economics of it..
And if you repair old comptuers you are goign to come up against an SMPU
sometime. And in many (but not all) of those there will eb considerable
non-isolated circuitry. So you have to know how to work on it safely.
-tony
11:03 p.m.
Oh Dear!
I seem to have stirred up a bit of a hornets nest. The facts are
clear. I related what went on at DEC whilst working there. My memory could
have been at fault. However another former DEC employee (Alison) also there
at the time in question corroborated what I had said with out any prompting
What the heck has that got to do with anything...
I stopped accepting the 'This is right because I say so' sort of arguemtn
when I was abotu 3 years old, and I have no intention of acceting it now.
It's very likely you and Ron are right, but, to quote the text over the
doorway of Kirkaldy's works in Southwark : 'Facts, not Opinions'.
How coue this didn't applit to the green CRT then?
Sure, I over-simplified it. What you really do is :
Check the mains tester on a known-live point.
Check the chassis is daed, but is receiving power, and/or the tester
lights on the live feed to the chassis, say on the dropping resistor.
Check the mains tester on a live point _again_
And then brush the chassi with the back of you fingers to check it's not
live. That wway you're thrown off if it is..
from me. That?s enough to establish it as something
that would pass any
evidential test legal or otherwise.
'Truth is often stranger that fiction'
Finally - perhaps I should have 'here's how I did it. You do what's best for
you.' I have four DEC screens once useless through blue spot working just
fine.
Regards
?
Rod Smallwood
?
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 04 April 2012 19:29
To: cctalk at classiccmp.org
Subject: Re: how do you crack (open) a Rainbow mono monitor?
On 04/03/2012 04:07 PM, Tony Duell wrote:
>> All well and good. One tiny point. I worked for DEC Terminals Product
Lin=
>> e
>> when those items where in current production.=20
>>
> I could counter that by saying that while you may well hvee(SP?)
designed
> things that used said CRT, and may have handled
the CRTs for many years,
> this does not mean you know exactly how the CRTs themselves were
> designed, and whether they remain sade(SP?) if you remvoe(SP?) the front
glass
layer
>
> I don't beelvie DEC designed the CRT, they bought it in. I am nto(SP?)
even
> sure all came from one manufacturer, in which
case it may well be that
> some CRRTs(SP?) are safe without the outer glass, some are not. _I_
don't
know, and
I'd rather not be showered in glass fagments to find out.
Your belief is not a factor, you didn't work for DEC.
Rod and I both worked for DEC, I also worked with the
terminals people
during the Vt220, VT24x and VT320 series. DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
I am scpetical. If only because the CRTs in every DEC terminal I've been
inside has been a standard part with a normal type number.
Also, no manufacturer uses custom parts if they can avoid it. An
of-the-shelf part is cheaper and supply is more certain. And there is
absolutelly nothign odd about the dispaly circuitry in any VT series
terminal, or the performance requireds (resolution, etc) to require a
custom-made CRT
It's very likely DEC talked ot the CRT manufacturers, of course. But
mainly yo determine whcih CRT(s) would be suitable.
Anotehr thing, even if the CRT was custom-designed, I doubt very much the
requirment would have included 'Must be implosion-saft if soem hacker
removes the outer glass layer'. It would me much more likely to state
something like 'The CRT must have integral implosion protection to
<standard>) and the manufactuer decides how to comply with that. Given
that, any modication to the CRT could invalidate it.
I'm old enough to rember and worked on old tVs
that didn't have such
a safety layer. It was never an issue. For sport my brothers would
As am I...
FWIW, though, no TV set sold to the public in the UK ever had a CRT
pointing at the viewer without some kind of implosion protection. The
earlists sets (pre-wr) mounted the CRT vertically wit hthe screen on top,
the picture was viewed in a mirror. If the CRT imploded, the gass spreyed
upwards.
Later sets with the CRT conventionally mounted had a laminated glas or
(later) perspex sheild in front of the CRT. THen came tension bands and
laminated faceplate CRTs. Now, safety was takne a lot less seriously back
then, but they thougt this was enough of a danger for it to be necessary
to do something about it. And CRT implosion was, and is, not common.
take the
tubes (CRT) from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. I've observed they
can be quite robust fromt he (SPELL!) front but quite fragile from the
neck side.
Sure, the scree nad flare are thick glass, they have to be to withstand
atmospheric pressure. It's darn hard to break them.
But that is not the point. We are not only worried about somebody hitting
the screen. The other daner is stresses in the glasss causing it to
fracture spontaneously. And that does happen (I have met a TV engineer
who had a CRT crack across the screen one day for no apparent reason).
That's the big problem it can happen without warning.
>> The tubes were just fine without the face plate and met all implosion
>> requirements. Some (Green I think) did not have them at all.=20
> Interesting. I am suprised there are any differentces(SP?) between the
CRt(case)
> other than the phosphor. Why was this? Did all
colours of CRT come from
> the same manufacturer?
>
> It probably is safe to run the CRT without the outer glass sheet, and I
am
sure you know
what you are doing.
It had to do with acceleration voltages and part since the added glass was
leaded to meet EU/TUV standards for X-ray radiation. [1] A common
way to do this was to use one of those neon tester
screwdrivers which would light up if touched on a live chassis. If so,
revese the mains conenctions. A _NOT FUNNY_ 'joke' was to convice the
newbie that if he took his screwdriver apart and turned the neon round,
it would then light on a dead chassis. (Of course it does no such thing,
it still lights on a live one).
Still dangerous as the mains line can still be intercepted. You do
learn to behave well
to live long. I alwas felt that anything mains powered without
isolation was designed to
kill anyone trying to repair them. Sort of the first generation
"No User Serviceable Components Inside".
Hmmm.. Although at least over here j-random-public would pull off the back
and swap valves...
To be honest, I don't mucu care for non-isolated TVs and radios. I much
prefer a nice mains transformer and parallel heaters. But I can see the
economics of it..
And if you repair old comptuers you are goign to come up against an SMPU
sometime. And in many (but not all) of those there will eb considerable
non-isolated circuitry. So you have to know how to work on it safely.
-tony
5 Apr
5 Apr
11:30 a.m.
Oh Dear!
I seem to have stirred up a bit of a hornets nest. The facts are
clear. I related what went on at DEC whilst working there. My memory coul=
d
have been at fault. However another former DEC employee (Alison) also the=
re
at the time in question corroborated what I had said with out any prompti=
ng
from me. That=92s enough to establish it as something that would pass an=
y
evidential test legal or otherwise.=20
My problem with all this is that DEC did not make their own CRTs for
these terminals/monitors. And even if they were custom-designed (which I
doubt), I am amost positive that the envelopes are stanedard. They are
the smae dimensions, have lugs in the same places, etc. So it's likely
the implosion protection was standard too.
I am sure DEC requried integral implosion protection on such CRTs, they
would have not complied with safety requirements otherwise. This could eb
done through a tension band, a laminated faceplate or probably other
methods.
Wht is not obvious to me is that if you alter the CRT in some way, such
as removign oen layer of a laminated faceplate, that it still remains
safe to use. Maybe it does. CRT data sheets/books are no help, they
simply say 'No attempt should ever be made to remove the outer glass
layer or the tension band' or words to that effect. No CRT manufactuer is
goign to state publically it's OK, in case some idiot does somehting
silly and gets injured . The liability is too great. An off-the-record
comment from somebody who'd worked for a CRT manufactuer [1] would be
interesting...
[1[ I know you worked for a regunner, but that's not quite hte smae
thing. Most regunning involves working on the thin glass at the back end
of the neck, not the screen/flare.
'Truth is often stranger that fiction'
Finally - perhaps I should have 'here's how I did it. You do what's best =
for
you.' I have four DEC screens once useless through blue spot working just
fine. =20
My worry is what happens if the glass fractures at some point in the
future. You might not be the one using the monitor then.
-tony
5:59 a.m.
Your belief is not a factor, you didn't work for
DEC.
Rod and I both worked for DEC, I also worked with the terminals people
during the Vt220, VT24x and VT320 series. ? DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
Since the 1970s, maybe even the late 60s, just about all CRTs were
semi-custom parts. The tube companies normally would work with a
manufacturer to fit the needed specs and tweak certain characteristics
at no extra cost. I am sure DEC was do so with the tubes they were
buying.
I'm old enough to rember and worked on old tVs
that didn't have such
a safety layer. ?It was never an issue. ?For sport my brothers would take
the
tubes (CRT) ?from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. ?I've observed they
can be quite robust fromt he front but quite fragile from the neck side.
I have wondered if the whole CRT safety glass issue was the result of
some sort of nationwide scare - the real reasons are probably lost to
time. The stories of tubes imploding and sending shards of glass out
the front like a shotgun sound fantastic - but it seems that really
never happened (I should say "never"). Even with the big 12 inch radar
scope tubes from World War 2 with the glass in the face much thinner
than those in the late 1940s or 50s tubes - the necks were always the
weak part and took all the damage.
--
Will
8:40 a.m.
On 5 Apr 2012 at 8:59, William Donzelli wrote:
I have wondered if the whole CRT safety glass issue
was the result of
some sort of nationwide scare - the real reasons are probably lost to
time. The stories of tubes imploding and sending shards of glass out
the front like a shotgun sound fantastic - but it seems that really
never happened (I should say "never"). Even with the big 12 inch radar
scope tubes from World War 2 with the glass in the face much thinner
than those in the late 1940s or 50s tubes - the necks were always the
weak part and took all the damage.
Good question. Our family 10" Philco (1948) had a sheet of glass in
front of the CRT, as did our 1953 large-screen RCA. I wonder if it
was more to protect the face of the CRT from being scratched by the
overzealous housekeeper.
Dig into an old RCA tube manual and I think it notes the CRTs without
special faceplate protection.
--Chuck
11:42 a.m.
On 5 Apr 2012 at 8:59, William Donzelli wrote:
Hmm.. If it is an 'urban legend' then its one that's spread through many
countries, UK, and European TVs all ahve some kind of implosion protection
too. And thais at a time when we didn't have ambulance-chasing lawyers,
The data books on CRTs from the 1960s (I have a few) make it very clear
tht you ahve to fit a separate implosion screen if you use CRTs without
implosion protection.
If the 'real' reason for the implosion screen was to protect the CRT from
the user, why was it dropepd when the CRTs had tension bands? Such
screens are just as easy to scratch.
And yes, CRTs can and do fractuer at the screen end. Not normall from
impact (as several people have sid, the neck breaks first) but because of
stresses in the glass. Not common, but presumably enough of a danger to
make it worth doing something about.
I guess ultimately what you do with your own CRT is up to you. If the
only risk was while you were doign the repari ,that woudl eb the end of
it. But IMHO it isn't. A modified CRT could fial at some point in the
future, and I'd rather not have an innocent bystander harmed.
-tony
I have wondered if the whole CRT safety glass
issue was the result of
some sort of nationwide scare - the real reasons are probably lost to
time. The stories of tubes imploding and sending shards of glass out
the front like a shotgun sound fantastic - but it seems that really
never happened (I should say "never"). Even with the big 12 inch radar
scope tubes from World War 2 with the glass in the face much thinner
than those in the late 1940s or 50s tubes - the necks were always the
weak part and took all the damage.
Good question. Our family 10" Philco (1948) had a sheet of glass in
front of the CRT, as did our 1953 large-screen RCA. I wonder if it
was more to protect the face of the CRT from being scratched by the
overzealous housekeeper.
Dig into an old RCA tube manual and I think it notes the CRTs without
special faceplate protection.
12:34 p.m.
On 5 Apr 2012 at 19:42, Tony Duell wrote:
Hmm.. If it is an 'urban legend' then its one
that's spread through
many countries, UK, and European TVs all ahve some kind of implosion
protection too. And thais at a time when we didn't have
ambulance-chasing lawyers, The data books on CRTs from the 1960s (I
have a few) make it very clear tht you ahve to fit a separate
implosion screen if you use CRTs without implosion protection.
My issue with saying that implosion was a clear danger was that the
sheet of glass isn't present on all 1940s sets. Could the glass
also have been intended for protection against the soft X-rays
emitted at the CRT face? Remember this was the time when HV
rectifiers and even output tubes were customarily placed in a metal
cage.
--Chuck
6 Apr
6 Apr
10:57 a.m.
On 5 Apr 2012 at 19:42, Tony Duell wrote:
Right,,,
Over here, no TV sets were actually made suring WW2. After that war, I
think all sets had implosion protection (I've certainly enver seen or
heard of one that doesn't).
I have heard there were quite serious injuries caused to aircraft radar
operators in the war if the CRT imploded. Of course looking at a CRT down
a viewing hood (about 6" from your face) is rather different from
watching a TV at a noraml viewing distance, but I wonder if it was
decided based on that to fit protectio nto all TVs.
Hmm.. If it is an 'urban legend' then its
one that's spread through
many countries, UK, and European TVs all ahve some kind of implosion
protection too. And thais at a time when we didn't have
ambulance-chasing lawyers, The data books on CRTs from the 1960s (I
have a few) make it very clear tht you ahve to fit a separate
implosion screen if you use CRTs without implosion protection.
My issue with saying that implosion was a clear danger was that the
sheet of glass isn't present on all 1940s sets. Could the glass also have been intended for protection against the
soft X-rays
emitted at the CRT face? Remember this was the time when HV
rectifiers and even output tubes were customarily placed in a metal
cage.
I think X-rays prodeuced with an accellerating votlkage of 12kV to 15kV
are pretty much harmless...
Over here, the line ouptu valve (horizontal output tube), booster diode
(damper) and EHT rectifier (HV rectifer?) were often in a shield, but it
was a fairly light aluminium thing. Not going to be much protection
against X-rays. I think it was more an RF shield. It was rarely a
complete enclosure anyway.
With colour sets, the shunt stabiliser triode was something of an X-ray
emitter (it had 25kV from anode to cathode and pased about 1mA). That was
often shielded fairly wall.
As for the implosion screen, glass or perspex is pretty much X-ray
transparent unless it's doped wuth lead or similar. And I've never heard
it was. I've not seen any X-ray warnings about running the CRT without
the implosion screen (e.g. when servicing the set).
-tony
12:22 p.m.
On 6 Apr 2012 at 18:57, Tony Duell wrote:
Over here, no TV sets were actually made suring WW2.
After that war, I
think all sets had implosion protection (I've certainly enver seen or
heard of one that doesn't).
Do you have access to a copy of RCA handbook HB-3 (the "big" tube
guide with all sorts of strange stuff)? I don't, but it would be
interesting to see what they said on the issue of implosion
protection.
--Chuck
12:36 p.m.
Do you have access to a copy of RCA handbook HB-3 (the
"big" tube
guide with all sorts of strange stuff)? I don't, but it would be
interesting to see what they said on the issue of implosion
protection.
http://www.pmillett.com/index.html
Try above link, they may have something on TV tubes. Ben.
2:38 p.m.
On 6 Apr 2012 at 13:36, ben wrote:
http://www.pmillett.com/index.html
Try above link, they may have something on TV tubes. Ben.
No, he hasn't scanned that section of HB-3. Shame that--in some
ways, it's the most interesting.
--Chuck
4:04 p.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On Fri, 6 Apr 2012, Tony Duell wrote:
I think X-rays prodeuced with an accellerating
votlkage of 12kV to 15kV
are pretty much harmless...
Over here, the line ouptu valve (horizontal output tube), booster diode
(damper) and EHT rectifier (HV rectifer?) were often in a shield, but it
was a fairly light aluminium thing. Not going to be much protection
against X-rays. I think it was more an RF shield. It was rarely a
complete enclosure anyway.
Low energy X-rays absorb very easily. According to this:
http://henke.lbl.gov/optical_constants/atten2.html
you get 1/e attenuation for 14keV X-rays for every 400 microns of
aluminium, so it doesn't take much thickness to block them entirely.
At 25keV, you need about 2.2mm aluminium, but just 100 microns of iron for
1/e attenuation.
Alexey
5:55 p.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On 6 Apr 2012 at 23:04, Alexey Toptygin wrote:
you get 1/e attenuation for 14keV X-rays for every 400
microns of
aluminium, so it doesn't take much thickness to block them entirely.
At 25keV, you need about 2.2mm aluminium, but just 100 microns of iron
for 1/e attenuation.
I've got to do some reading--I remember that "aluminized" screens
started to be included in the 1950s. I wonder if that had to do with
X-rays.
--Chuck
6:40 p.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On Fri, 6 Apr 2012, Chuck Guzis wrote:
On 6 Apr 2012 at 23:04, Alexey Toptygin wrote:
I doubt it - aluminium is not the best X-ray absorber. Lead (and leaded
glass) is much better.
Alexey
you get 1/e attenuation for 14keV X-rays for
every 400 microns of
aluminium, so it doesn't take much thickness to block them entirely.
At 25keV, you need about 2.2mm aluminium, but just 100 microns of iron
for 1/e attenuation.
I've got to do some reading--I remember that "aluminized" screens
started to be included in the 1950s. I wonder if that had to do with
X-rays.
7 Apr
7 Apr
11:42 a.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
I've got to do some reading--I remember that
"aluminized" screens
started to be included in the 1950s. I wonder if that had to do with
X-rays.
I don't see how it can do.
X=ray emission occurs when the electron is decelerated -- when it hits
the screen, basically. Now, you need the electrons to hit the phosphor
(in front of the aluminium layer) to excite it, so you actually get a
visible glow. That means the X-rays would be produced in front of the
aluminium layer...
Aluminising had 2 main purposes :
1) Althoguh the electrons could get throug it to hit the phosphor,
heavier ions could not. This protected the phospohr from damage, and
stopped a problem called 'ion burn' where you got a dark spot or X in the
middle fo the screen. Before that, the normal way to prevent ion burn was
to have a bent electron gun with a small external magnet to dedirec the
electron beam along the CRT axis. THe ions were not much effected by this
magnetic field and so they ended up hitting one of the gun electrodes or
the wall of the CRT. The magnet assembly was known (at least over here)
as the 'ion trap', and if it was not properly postioned you coudl end up
with no image on the screen at all.
2) It acts as a light reflector, so most of the light emitted by the
phosphor comes out of the front of the CRT. No point in easting it by
illumninating the inside of the set :-)
I _think_ almost all electromagnetlcally-deflected CRTs used in classic
computers, certainly the onses used in DEC termninals, etc, will be
aluminised.
-tony
1:47 p.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On 7 Apr 2012 at 19:42, Tony Duell wrote:
2) It acts as a light reflector, so most of the light
emitted by the
phosphor comes out of the front of the CRT. No point in easting it by
illumninating the inside of the set :-)
I think that's probably it. A couple of datasheets out of HB-3 would
certainly answer the question, but I'll see if I can find the answer
elsewhere. My cherished set of HB-3 disappeared during a move with a
bunch of other notable books. :(
--Chuck
8 Apr
8 Apr
11:29 a.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On 7 Apr 2012 at 19:42, Tony Duell wrote:
No, the primary reason for aluminising the screen was certainly to
prevent -ve ions (from residual gas in the CRT) from damaging the
phosphor .This was a real problem at one time. The ions were not
deflectred much by the magnetic defleciton system (they would be by
electrostatic defleciton plates IIRC), and you ended up with a dark spot
at the centre of the screen.
I guess few people remember fitting and adjusting the ion trap magnet on
a monochorm TV set...
I've found an old Mazda databook. This has nothing to do wit hte car
company, it states that 'Mazda Cathode Ray Tubes are manufacutred in
Great Britain for the British Thomson-Houston Co, Ltd, London and Rugby,
and distributed by The Edison Swan Electric Co Ltd'
Anywy, this book contains data sheets on 3 CRTs, CRM71, CRM91 and CRM
121. They are very similar apart from the screen diameter which is 7", 9"
and 12" respectively. These are circular-screen magnetically defelcted
CRTs for TV applications, and if what I think is a date _is_ a date, the
data sheets were printed in 1942 (which does suprise me a bit).
All 3 data sheets contain a paragrpah simular to the following (obviously
the type number changes) :
'The handling of the CRM71 tube in transportation, storage and use
requires car, because the tube may be broken if subjected to sudden jars
or excessive strains or, if abused, the tube may be weakened so that it
may subsequently implode owing to the pressure on the tube due to the
vacuum within. The equipment in which the cathode ray tube is utilised
should be designed to prevent the bulb from being damaged and to protect
the user from the effects of an implosion if the bulb is damaged or has
been weakened in prior handling. The screen of the tube should be covered
with a plate of safety glass, and googles worn when handling the tube'
Now, thoughts.. .THis is round screen CRT with a noticeably convex screen
(commonly known a sa 'goldfish bowl' over here ;-)). SUch a screen is
stronger for a given glass thichness than a flatter one, so the glass
could be a lot thinner than on a more modern CRT. THis may mean it's more
liable to fracture into sharp fracgments that fly.
Thre is not integral implosion protection on this CRT.
And the nrequirement for having implosion protection was noted quite
early on (if my interpetation that this was printed in 1942 is correct).
-tony
2) It acts as a light reflector, so most of the
light emitted by the
phosphor comes out of the front of the CRT. No point in wasting it by
illumninating the inside of the set :-)
I think that's probably it. A couple of datasheets out of HB-3 would 
9 Apr
9 Apr
2:29 a.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On Sun, 8 Apr 2012, Tony Duell wrote:
I guess few people remember fitting and adjusting the
ion trap magnet on
a monochorm TV set...
Don't need to remember, I have two such sets (both much older than me) ;-)
Christian
11:21 a.m.
New subject: X-ray safety Re: how do you crack (open) a Rainbow mono monitor?
On Sun, 8 Apr 2012, Tony Duell wrote:
I see...
I doubt there are many such sets still in use over here. They'd be Systam
A (405 line) which means they'd need a converter to use with Systme I
signals (or the outptu of a digital TV receiver). Oh well...
Incidentalyl, when I looked at those CRT data sheets yesterday, the same
book contains recomended circuits for 'high defintion TV timebases'.
That's 405 line 'high defintion' of coruse :-)
-tony
I guess few people remember fitting and adjusting
the ion trap magnet on
a monochorm TV set...
Don't need to remember, I have two such sets (both much older than me) ;-)
7 Apr
7 Apr
11:02 p.m.
In the UK there was a minimal television service in the late 1940's.
(Started 1937 closed down in 1939 resumed 1948/9)
What really kicked it off was the end of rationing and the Queens coronation
in 1953. I am old enough to have watched the coronation in Liverpool on TV.
Well sort of TV. My Father worked at the Army Anti-Aircraft depot in
Daysbrook Lane in Liverpool. The guns were guided by radar and one of the
technical types had converted a surplus 9" Radar display to show TV.
Sound? They just turned the radio on!
For many years I thought our Queen was a sort of orange colour.
Regards
?
Rod Smallwood
?
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of Tony Duell
Sent: 06 April 2012 18:58
To: cctalk at classiccmp.org
Subject: Re: how do you crack (open) a Rainbow mono monitor?
On 5 Apr 2012 at 19:42, Tony Duell wrote:
Right,,,
Over here, no TV sets were actually made suring WW2. After that war, I
think all sets had implosion protection (I've certainly enver seen or
heard of one that doesn't).
I have heard there were quite serious injuries caused to aircraft radar
operators in the war if the CRT imploded. Of course looking at a CRT down
a viewing hood (about 6" from your face) is rather different from
watching a TV at a noraml viewing distance, but I wonder if it was
decided based on that to fit protectio nto all TVs.
Hmm.. If it is an 'urban legend' then its
one that's spread through
many countries, UK, and European TVs all ahve some kind of implosion
protection too. And thais at a time when we didn't have
ambulance-chasing lawyers, The data books on CRTs from the 1960s (I
have a few) make it very clear tht you ahve to fit a separate
implosion screen if you use CRTs without implosion protection.
My issue with saying that implosion was a clear danger was that the
sheet of glass isn't present on all 1940s sets. Could the glass also have been intended for protection against the
soft X-rays
emitted at the CRT face? Remember this was the time when HV
rectifiers and even output tubes were customarily placed in a metal
cage.
I think X-rays prodeuced with an accellerating votlkage of 12kV to 15kV
are pretty much harmless...
Over here, the line ouptu valve (horizontal output tube), booster diode
(damper) and EHT rectifier (HV rectifer?) were often in a shield, but it
was a fairly light aluminium thing. Not going to be much protection
against X-rays. I think it was more an RF shield. It was rarely a
complete enclosure anyway.
With colour sets, the shunt stabiliser triode was something of an X-ray
emitter (it had 25kV from anode to cathode and pased about 1mA). That was
often shielded fairly wall.
As for the implosion screen, glass or perspex is pretty much X-ray
transparent unless it's doped wuth lead or similar. And I've never heard
it was. I've not seen any X-ray warnings about running the CRT without
the implosion screen (e.g. when servicing the set).
-tony
8 Apr
8 Apr
11:40 a.m.
New subject: how do you crack... Homebrew TV
On 4/8/2012 12:02 AM, Rod Smallwood wrote:
In the UK there was a minimal television service in the late 1940's.
(Started 1937 closed down in 1939 resumed 1948/9)
What really kicked it off was the end of rationing and the Queens coronation
in 1953. I am old enough to have watched the coronation in Liverpool on TV.
Well sort of TV. My Father worked at the Army Anti-Aircraft depot in
Daysbrook Lane in Liverpool. The guns were guided by radar and one of the
technical types had converted a surplus 9" Radar display to show TV.
Sound? They just turned the radio on!
For many years I thought our Queen was a sort of orange colour.
Regards
Rod Smallwood
The QUEEN is GREEN. See here. 2" green crt.
http://www.freewebs.com/cameramanlink/electronicsprojects.htm
Ben.
7 Apr
7 Apr
11:12 p.m.
There seems to a wide belief that when implosion occurs on a CRT it's always
the front that is breached. Not so, any part of a CRT can fail and its still
an implosion.
Regards
?
Rod Smallwood
?
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of William Donzelli
Sent: 05 April 2012 13:59
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: how do you crack (open) a Rainbow mono monitor?
Your belief is not a factor, you didn't work for
DEC.
Rod and I both worked for DEC, I also worked with the terminals people
during the Vt220, VT24x and VT320 series. ? DEC actually did interact
with CRT designers to get the exact product they wanted to DEC
specifications.
Since the 1970s, maybe even the late 60s, just about all CRTs were
semi-custom parts. The tube companies normally would work with a
manufacturer to fit the needed specs and tweak certain characteristics
at no extra cost. I am sure DEC was do so with the tubes they were
buying.
I'm old enough to rember and worked on old tVs
that didn't have such
a safety layer. ?It was never an issue. ?For sport my brothers would take
the
tubes (CRT) ?from junkers and haul them out back where they would
stand back 20-30 feet and pelt them with rocks. ?I've observed they
can be quite robust fromt he front but quite fragile from the neck side.
I have wondered if the whole CRT safety glass issue was the result of
some sort of nationwide scare - the real reasons are probably lost to
time. The stories of tubes imploding and sending shards of glass out
the front like a shotgun sound fantastic - but it seems that really
never happened (I should say "never"). Even with the big 12 inch radar
scope tubes from World War 2 with the glass in the face much thinner
than those in the late 1940s or 50s tubes - the necks were always the
weak part and took all the damage.
--
Will
31 Mar
31 Mar
10:54 a.m.
It's been a while, but I think there is a round plastic cap on the
back that can be popped off. There is a screw behind it, and removing
that should lossen the rear cover. If there is a leveler post there it
might have to be fully extended.
Paul
On Sat, Mar 31, 2012 at 3:20 AM, Chris M <chrism3667 at yahoo.com> wrote:
for the purpose of expunging the screen rot. Need to get behind the screen thingee there
noon
for the purpose of expunging the screen rot. Need to get behind the screen thingee there
First extend the little leg as far as it will go (put the monitor the
right way up and press the button on the side, them lift the back edge).
With the leg extended. put the monitor face-down. On the back there's a
circular plastic cap. Prise (Pry?) this off wit ha screwdriver and undo
the screw thus exposed. Then lift off the cassing.
From what I remember, and it's been years since
I've been inside one,
theres a single PCB on the top (component-side down) and
the CRT. I think
you have to discharge and disconnect the anode connector from the CRT and
remvoe the CRT base connector. I can't remember how the yoke is conencted
ot the PCB, it's it's plugged in, it's easy, if it's hardwired, I'd
desolder the wires rather than removign the yoke from the CRT at this
stage.
Then remvoe the PCB screws and the PCB, I think 4 more screws retain the
chassins metalwork and the CRT, it then all comes apart.
Be careful if you are tryign to cure screen rot. I am sure the second
faceplate layre in this monitor is part of the implosion protection
ssytem, and the idea of removing it and leaving it out, or not proeprly
bonding it to the CRT envelope would seem to produce a dangerous monitor.
-tony
4640
days inactive
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61 comments
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