30 Jan
2011
30 Jan
'11
2:12 a.m.
Had another ADM3a come in, again with severe screen rot.
Unlike the first time i now have successfully separated the faceplate from the CRT.
Question is of course how to get it back on again.
Anybody successfully done this ?
I know screenrot has come up often here, but I do not believe someone presented a working
solution yet.
Jos Dreesen
30 Jan
30 Jan
5:49 a.m.
On Sun, 30 Jan 2011, Jos Dreesen wrote:
Had another ADM3a come in, again with severe screen
rot.
Unlike the first time i now have successfully separated the faceplate from
the CRT.
Question is of course how to get it back on again.
Anybody successfully done this ?
What method did you use to remove the shield? I'd like to try this on
a HP 2647A.
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
5:58 a.m.
On 01/30/2011 02:49 PM, Mike Loewen wrote:
On Sun, 30 Jan 2011, Jos Dreesen wrote:
A thin flexible metal ruler and lots of time (2-3 hrs).
Jos
Had another ADM3a come in, again with severe
screen rot.
Unlike the first time i now have successfully separated the faceplate from the CRT.
Question is of course how to get it back on again.
Anybody successfully done this ?
What method did you use to remove the shield? I'd like to try this on a HP
2647A.
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
7:01 a.m.
From: jdr_use at bluewin.ch
On 01/30/2011 02:49 PM, Mike Loewen wrote:
Hi
I'm told a thin piece of music wire or guitar string
is what to use.
Most just leave the shield off. I'm not sure if one
could replace is without some heavy duty vacuum
equipment.
Dwight
On Sun, 30 Jan 2011, Jos Dreesen wrote:
A thin flexible metal ruler and lots of time (2-3 hrs).
Jos
Had another ADM3a come in, again with severe
screen rot.
Unlike the first time i now have successfully separated the faceplate from the CRT.
Question is of course how to get it back on again.
Anybody successfully done this ?
What method did you use to remove the shield? I'd like to try this on a HP 2647A.
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
31 Jan
31 Jan
10:45 a.m.
dwight elvey wrote:
Hi
I'm told a thin piece of music wire or guitar string
is what to use.
Most just leave the shield off. I'm not sure if one
could replace is without some heavy duty vacuum
equipment.
Dwight
For an HP, I used some suitable resistance wire and a 12V DC power supply - it
ran hot enough to assist with 'sawing' through the bond between faceplate and
CRT, but not *too* hot (that being a subjective thing, but doubtless I could
have used something with more power and done the job far more quickly, but I
didn't want to put too much localised heat into the tube)
Faceplate was reattached with just an air gap and some clear caulk around the
very edges.
cheers
Jules
1 Feb
1 Feb
12:25 a.m.
I have managed to remove the outer screen on a couple of DEC VR201's that
had the blue spot rot. I sacrificed the outer screen and removed the soft
layer beneath. It's this layer that has the problem.
Breaking the glass sounds a bit drastic but there's no way to put it back.
The tube goes back in the case and you can re-site the rubber stand-offs to
maintain the gap that now exists around the face of the tube.
Regards
?
Rod Smallwood
?
Old |d|i|g|i|t|a|l| always wanted.
?
-----Original Message-----
From: cctech-bounces at classiccmp.org [mailto:cctech-bounces at classiccmp.org]
On Behalf Of dwight elvey
Sent: 30 January 2011 15:01
To: General Discussion: On-Topic and Off-Topic Posts
Subject: RE: ADM3a screen rot again...
Hi
I'm told a thin piece of music wire or guitar string
is what to use.
Most just leave the shield off. I'm not sure if one
could replace is without some heavy duty vacuum
equipment.
Dwight
=
From: jdr_use at bluewin.ch
On 01/30/2011 02:49 PM, Mike Loewen wrote:
HP
2647A.
On Sun, 30 Jan 2011, Jos Dreesen wrote:
> Had another ADM3a come in, again with severe screen rot.
> Unlike the first time i now have successfully separated the faceplate
from the
CRT.
>> Question is of course how to get it back on again.
>> Anybody successfully done this ?
>
> What method did you use to remove the shield? I'd like to try this on a
Mike Loewen mloewen at cpumagic.scol.pa.us
Old Technology http://sturgeon.css.psu.edu/~mloewen/Oldtech/
A thin flexible metal ruler and lots of time (2-3 hrs).
Jos
11:24 a.m.
I have managed to remove the outer screen on a couple of DEC VR201's =
that
had the blue spot rot. I sacrificed the outer screen and removed the =
soft
layer beneath. It's this layer that has the problem.
Breaking the glass sounds a bit drastic but there's no way to put it =
back.=20
The tube goes back in the case and you can re-site the rubber stand-offs =
to
maintain the gap that now exists around the face of the tube.=20
Are you sure that that faceplate and the 'soft layer' doens't act as a
support for broken glass in the event of an implosion. Certainly some CRT
data books imply otherwiese...
I would not want to use a VR201 that could implode in my face!
-tony
31 Jan
31 Jan
5:36 a.m.
--- On Sun, 1/30/11, Jos Dreesen <jdr_use at bluewin.ch> wrote:
Had another ADM3a come in, again with
severe screen rot.
Unlike the first time i now have successfully separated the
faceplate from the CRT.
Question is of course how to get it back on again.
Anybody successfully done this ?
I know screenrot has come up often here, but I do not
believe someone presented a working solution yet.
I'm pretty sure I've posted about it before. But, basically, once you've
cleaned all the gunky PVA compound off the face of the tube and the back of the faceplate,
you just stick the faceplate back on with packing tape around the edges.
The "screen rot" problem is real common with those of us that collect old TV
sets - the same thing happens to old color picture tubes (21FJP22, etc). It's
frequently called "cataracts". To remove the faceplate on those tubes, take the
tube out and put it in a bucket or something that supports it by the bell, protecting the
neck and allowing you to work on the face. Then, heat the faceplate with a heat gun to
soften the PVA. Sometimes you can get it to just fall off, other times it takes prodding.
Careful not to break the faceplate, and wear goggles (just in case something goes FOOMP!)
There are different kinds of PVA compound - Zenith made tubes have one that does not
soften with heat. That you have to slice off with wire - I know some people use a nichrome
wire powered by a car battery.
Another trick I've heard of is to simply let the tube sit face down in water for a few
weeks. Never tried it though.
In the ADM3's I have done, the PVA was already so bad that the faceplate practically
fell off.
Once you have it all clean, just put the faceplate back on, secured at the edges with
packing tape or similar. It's tinted, and improves contrast.
Technically, the faceplate is bonded as a means to help hold the faceplate together in the
event of implosion, and I don't have any idea if just having it taped over the front
will do any good. In any event, I don't expect a modern tube like the ADM3's to
simply go FOOMP for no good reason.
Also, if the tube is really bad, you can replace it with one from a black and white
television set. Same pinout.
-Ian
3:50 p.m.
On 31/01/11 13:36, Mr Ian Primus wrote:
Careful not to break the faceplate, and wear goggles
(just in case something goes FOOMP!)
Hm. I'd be more worried about flying glass shards hitting a major
artery. Death by massive blood loss can't be much fun, and AIUI survival
rates are pretty slim even with prompt first aid. Medium-low likelihood,
but very, *very* high risk.
If I was doing this, I'd be using a nice, big metal face-shield (similar
to those used for welding), REALLY THICK clothing and similarly thick
gloves. At least then any glass shards would have to be pretty damn huge
(and flying with considerable energy at short distance) to do any major
damage.
Though that said -- don't most CRTs have an anti-implosion band, which
is intended to stop the glass from spreading out? Or are these CRTs too
old (or small?) for that?
Though AIUI blowing out a CRT from the front would involve significant
force... along the lines of BB guns or rifles, not small tools dropped
on the tube face... I know the DG7/32 scope tube in my spares box has a
decently thick face vs. the neck thickness (looks to be a good 1cm
thick), and that's only a 7cm round-face tube. I'd imagine a 14in or
17in raster-scan tube would have a similarly thick face plate, if not
thicker.
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
4:26 p.m.
Though that said -- don't most CRTs have an
anti-implosion band, which is
intended to stop the glass from spreading out? Or are these CRTs too old (or
small?) for that?
Nearly all CRTs built past the late 1950s really are not all that
dangerous, unlike the thin walled CRTs of the World War 2 vintage. The
glass in the bell is really tough stuff, and is far thicker than it
needs to be. Even if you drop a good sized CRT, it will generally
break where the bell and neck join first, and the neck will get sucked
into the bell. If and when the glass in the bell cracks, the vacuum is
already well on its way to atmospheric pressure.
As a kid, I tried to abuse many CRTs found in old TV sets, and was
always disappointed at how unspectacularly they break.
Really, use caution when handling the things, but don't go overboard.
--
Will
1 Feb
1 Feb
5:40 a.m.
William Donzelli wrote:
Yes, they're pretty tough. For CRTs with a metal band around the edge, I don't
think the faceplate is essential. Yes, it's additional protection if the tube
does blow, and also handy to protect the tube from something thrown at it
(although it'd have to be something heavy given how thick the glass at the
front of the tube is!) - but I don't think the risk is made significantly
higher by not having it (or not having it bonded to the CRT).
I've heard that sometimes the faceplate function is more cosmetic, too - there
to improve contrast, reduce glare, make the tube front seem flatter than it
actually is etc.
cheers
Jules
Though that
said -- don't most CRTs have an anti-implosion band, which is
intended to stop the glass from spreading out? Or are these CRTs too old (or
small?) for that?
Nearly all CRTs built past the late 1950s really are not all that
dangerous, unlike the thin walled CRTs of the World War 2 vintage. The
glass in the bell is really tough stuff, and is far thicker than it
needs to be. Even if you drop a good sized CRT, it will generally
break where the bell and neck join first, and the neck will get sucked
into the bell. If and when the glass in the bell cracks, the vacuum is
already well on its way to atmospheric pressure.
As a kid, I tried to abuse many CRTs found in old TV sets, and was
always disappointed at how unspectacularly they break.
11:19 a.m.
On 31/01/11 13:36, Mr Ian Primus wrote:
Careful not to break the faceplate, and wear
goggles (just in case something goes FOOMP!)
Hm. I'd be more worried about flying glass shards hitting a major
artery. Death by massive blood loss can't be much fun, and AIUI survival
rates are pretty slim even with prompt first aid. Medium-low likelihood,
but very, *very* high risk.
If I was doing this, I'd be using a nice, big metal face-shield (similar
to those used for welding), REALLY THICK clothing and similarly thick
gloves. At least then any glass shards would have to be pretty damn huge
(and flying with considerable energy at short distance) to do any major
damage.
Though that said -- don't most CRTs have an anti-implosion band, which
is intended to stop the glass from spreading out? Or are these CRTs too
old (or small?) for that?
Though AIUI blowing out a CRT from the front would involve significant
force... along the lines of BB guns or rifles, not small tools dropped
on the tube face... I know the DG7/32 scope tube in my spares box has a
decently thick face vs. the neck thickness (looks to be a good 1cm
thick), and that's only a 7cm round-face tube. I'd imagine a 14in or
17in raster-scan tube would have a similarly thick face plate, if not
thicker.
--
Phil.
classiccmp at philpem.me.uk
http://www.philpem.me.uk/
4844
days inactive
4846
days old
11 comments
9 participants
participants (9)
-
ard＠p850ug1.demon.co.uk -
classiccmp＠philpem.me.uk -
dkelvey＠hotmail.com -
ian_primus＠yahoo.com -
jdr_use＠bluewin.ch -
jules.richardson99＠gmail.com -
mloewen＠cpumagic.scol.pa.us -
rodsmallwood＠btconnect.com -
wdonzelli＠gmail.com