1 Dec
2013
1 Dec
'13
12:26 p.m.
I recently "saved" a small pile of VT220 and VT100 terminals from a
barn in western WI. They were grubby and have various issues but I am
enjoying cleaning them up and making a few good ones from some bad ones.
One of the VT220 is a very new vintage unit. Circa-1987, with some
components with date codes 1990. It has a totally different logic
board than earlier models I've worked on-- this one having a large PLCC
package in the center of the board which I assume is a custom device
integrating the video controller and much of the support logic since
there are considerably fewer parts on this board than the older ones.
Still an 8031 CPU though.
This unit also has a totally different video monitor circuit than the
older ones and my problem lies somewhere on that board-- I am getting
a very dim image even though the CRT itself appears to be in very good
shape with no burn-in and otherwise crisp display. I think I've got a
high-voltage problem but without schematics to match this board, it's
kind of a crap shoot to start debugging.
So, wondering if anyone has newer schematics or technical reference for
the VT220 than we find out on bitsavers? The bitsavers docs are circa-
1983 so I am looking for something 1987 or later when it appears they
did a considerable redesign of the guts of this terminal.
Chris
--
Chris Elmquist
1 Dec
1 Dec
1:18 p.m.
Been a while since I worked on CRTs on my video games... but IIRC if
the HV drops the picture will bloom as the yoke can deflect the beam
further before the electrons strike the face. If your picture is sharp
but dim, my first guess would not be an HV problem. When I was working
on my arcade games, I picked up for a pretty good price a voltage probe
for CRTs.
Have you measured the filament voltage to the CRT ? not sure what
VT220s would be, but I IIRC on arcade stuff is is I think 6.3V.
Are you able to easily swap a tube to see that the dim problem follows
the electronics and not the tube ?
-- Curt
On 2013-12-01 15:26, Chris Elmquist wrote:
I recently "saved" a small pile of VT220 and
VT100 terminals from a
barn in western WI. They were grubby and have various issues but I
am
enjoying cleaning them up and making a few good ones from some bad
ones.
One of the VT220 is a very new vintage unit. Circa-1987, with some
components with date codes 1990. It has a totally different logic
board than earlier models I've worked on-- this one having a large
PLCC
package in the center of the board which I assume is a custom device
integrating the video controller and much of the support logic since
there are considerably fewer parts on this board than the older ones.
Still an 8031 CPU though.
This unit also has a totally different video monitor circuit than the
older ones and my problem lies somewhere on that board-- I am
getting
a very dim image even though the CRT itself appears to be in very
good
shape with no burn-in and otherwise crisp display. I think I've got
a
high-voltage problem but without schematics to match this board, it's
kind of a crap shoot to start debugging.
So, wondering if anyone has newer schematics or technical reference
for
the VT220 than we find out on bitsavers? The bitsavers docs are
circa-
1983 so I am looking for something 1987 or later when it appears they
did a considerable redesign of the guts of this terminal.
Chris
6:27 p.m.
On Sunday (12/01/2013 at 04:18PM -0500), rescue wrote:
Been a while since I worked on CRTs on my video games... but IIRC if
the HV drops the picture will bloom as the yoke can deflect the beam
further before the electrons strike the face. If your picture is
sharp but dim, my first guess would not be an HV problem. When I
was working on my arcade games, I picked up for a pretty good price
a voltage probe for CRTs.
Have you measured the filament voltage to the CRT ? not sure what
VT220s would be, but I IIRC on arcade stuff is is I think 6.3V.
Are you able to easily swap a tube to see that the dim problem
follows the electronics and not the tube ?
yes! Thanks Curt. I did swap the tube after posting the message and sure
enough, it was the tube after all. With a new tube, (see my messages
from a couple weeks ago where we saved NOS tubes from
the scrapper!) it
works like a charm.
So, I'm sure Tony will be all over me for swapping stuff before measuring
stuff but in this case, it panned out pretty well :-)
Would still like to find prints for this newer VT220 design but can move
forward now without them.
Chris
--
Chris Elmquist
2 Dec
2 Dec
2:08 p.m.
So, I'm sure Tony will be all over me for swapping
stuff before measuring
stuff but in this case, it panned out pretty well :-)
Would I???
One of my _old_ books on TV repair says that. faced with a blank screen,
novices often suspect the CRT. And that while, if the screen is blank, it
is unlikely there are any votlages present that would damage a
replacement CRT, swappign a CRT takes al ot of tiem, and it's best to get
out of that habit :-)
As I said in my first message, I think I would have measured all the CRT
electrode votlages first. The ones on the base pins are under 1kV, so a
noraml multimeter will do. The EHT is goign to be 12-15kV, so you need a
special EHT probe or meter.
If the votlags ahd been normal, I might have tired turning up the
'screen' (first anode) preset to see if I could coax a bit more emission
out of the CRT.
-tony
3:17 p.m.
On Monday (12/02/2013 at 10:08PM +0000), Tony Duell wrote:
Thanks Tony. Of course I am just teasing you since I have seen previous
postings where you scold folks for randomly swapping parts without a plan.
I fully understand and appreciate that.
In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. The only thing I liked about it was
that it was amber and all of my replacements are white or green. But,
so goes it.
With the new tube connected and no other adjustments made, the display
is bright and crisp and I have plenty of contrast adjustment with the
contrast control.
I've swapped CRTs in two VR201 and one VT220 in the past couple weeks
so I am getting it down to a science now :-)
In any case, while going down this path I did discover the lack of
documentation for the newer VT220 design and so wrapped the request for
that together with the debug of this particular "dim" unit.
Chris
--
Chris Elmquist
So, I'm
sure Tony will be all over me for swapping stuff before measuring
stuff but in this case, it panned out pretty well :-)
Would I???
One of my _old_ books on TV repair says that. faced with a blank screen,
novices often suspect the CRT. And that while, if the screen is blank, it
is unlikely there are any votlages present that would damage a
replacement CRT, swappign a CRT takes al ot of tiem, and it's best to get
out of that habit :-)
As I said in my first message, I think I would have measured all the CRT
electrode votlages first. The ones on the base pins are under 1kV, so a
noraml multimeter will do. The EHT is goign to be 12-15kV, so you need a
special EHT probe or meter.
If the votlags ahd been normal, I might have tired turning up the
'screen' (first anode) preset to see if I could coax a bit more emission
out of the CRT.
3 Dec
3 Dec
11:52 a.m.
Thanks Tony. Of course I am just teasing you since I
have seen previous
postings where you scold folks for randomly swapping parts without a plan.
YEs, and I still do :-).
I fully understand and appreciate that.
Fortunately, as I said, it is unlikely that a good CRT would be amaged by
putting it into siad terminal. It's just that it takes a long time ot
swap it, and you're wasting the time if that's not the fault.
I said 'unlikely' to damage the new CRT. Actually, those all-glass pin
bases are somwaht fragile, and continually fitting and remvoig nthe
socket may damage a seal. I've ruined a few B7G andB99A (7 pin miniature
and Noval) vlaves over the years in this way. So it's best not to remvoe
the CRT without a good reason.
In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. The only thing I liked about it was
Oh, I must have mis-read what you said. I thought you sid the CRT looked
perfect.
that it was amber and all of my replacements are white
or green. But,
so goes it.
A white one and a colour filter :-)
The old CRT might take being boosted. It's unlikely, modern-ish CRETs
don;'t normally repsond too well, but if the CRT is dead anyway, you
can't make things much worse. BASically, over-run the heater as much as
you dare (15 or 18V) and apply a high votlage (a few hundred volts) with
a current limiting resisotr (a few mA) between the carthode and control
grid (grid +ve in this case). There ahve been designes for CRT boosters
in various magazines over the years, there are probably designs on the web.
The idea is to rip the top layer off the cathode, exposing better
emissive material. Problem is that modern cathodes don't have much left
if you try this. You may well end up with a CRT that gies no emission at all.
In any case, while going down this path I did discover
the lack of
documentation for the newer VT220 design and so wrapped the request for
I don't thing I've seen that one. The VT220s I've worked onhad all the
ICs in DIL packages. I do recall PLCC ICs in the VT3xx terminals, I
wonder if the design is similar ot one of thsoe.
-tony
4 Dec
4 Dec
1:52 a.m.
On Tue, 3 Dec 2013, Tony Duell wrote:
Then I must have mis-read, too. I thought he said that the terminal was
in its original box and had a pristine looking CRT.
Christian
In this case,
the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. The only thing I liked about it was
Oh, I must have mis-read what you said. I thought you sid the CRT looked
perfect.
6:25 a.m.
On Wed, 4 Dec 2013, Christian Corti wrote:
Then I must have mis-read, too. I thought he said that
the terminal was in
its original box and had a pristine looking CRT.
The box was an imagination, but otherwise:
"I am getting a very dim image even though the CRT itself appears to be in
very good shape with no burn-in and otherwise crisp display. I think I've
got a high-voltage problem[...]"
is in contradiction to this:
"In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. "
Christian
7:08 a.m.
On Wed, 4 Dec 2013, Christian Corti wrote:
The box was an imagination, but otherwise:
"I am getting a very dim image even though the CRT itself appears to be in
very good shape with no burn-in and otherwise crisp display. I think I've
got a high-voltage problem[...]"
is in contradiction to this:
"In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. "
One statement was after the other. But usually, burn-in takes longer than
that.
7:59 a.m.
On Wednesday (12/04/2013 at 07:08AM -0800), Fred Cisin wrote:
On Wed, 4 Dec 2013, Christian Corti wrote:
Hmm... ya. I apologize. I have two terminals on the bench and I've
mixed up the stories between the two. I swamped the tube in a second
one that did have burn-in and a very similar dim image problem. With the
new tube, it works great and so the electronics are good and it gets to
keep the new tube.
The other VT220, which is the one with the newer logic board and newer
monitor electronics has a dim image but that tube is not burned in at all.
It looks brand new. I have not swapped the tube on that unit yet.
So, sorry. I clearly confused things even for myself.
Chris
--
Chris Elmquist
The box was an imagination, but otherwise:
"I am getting a very dim image even though the CRT itself appears to be in
very good shape with no burn-in and otherwise crisp display. I think I've
got a high-voltage problem[...]"
is in contradiction to this:
"In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. "
One statement was after the other. But usually, burn-in takes longer than
that.
11:23 a.m.
On Wednesday (12/04/2013 at 11:03AM -0800), Fred Cisin wrote:
On Wed, 4 Dec 2013, Chris Elmquist wrote:
Ahem. Yes. Here in The Land of 10,000 Lakes, when they started making
it difficult to get rid of old electronics and particularly TVs, swamping
them was a sad but popular disposal method.
In any case, Tony is also an excellent typing teacher.
--
Chris Elmquist
Hmm... ya. I apologize. I have two terminals on
the bench and I've
mixed up the stories between the two. I swamped the tube in a second
We can assume how Tony would feel about tube SWAMPING :-) 
4:51 p.m.
On 12/04/2013 01:23 PM, Chris Elmquist wrote:
On Wednesday (12/04/2013 at 11:03AM -0800), Fred Cisin
wrote:
At least here in the northern part of the Land of 10,000 Lakes, the local
dumps will take old electronics - including CRT TVs and monitors - for
free, as long as they're from a household rather than business. I expect it
was in response to too many items turning up in swamps :-)
cheers
Jules
On Wed, 4 Dec 2013, Chris Elmquist wrote:
Ahem. Yes. Here in The Land of 10,000 Lakes, when they started making
it difficult to get rid of old electronics and particularly TVs, swamping
them was a sad but popular disposal method. Hmm... ya. I apologize. I have two terminals on
the bench and I've
mixed up the stories between the two. I swamped the tube in a second
We can assume how Tony would feel about tube SWAMPING :-)
2:31 p.m.
On Wed, 4 Dec 2013, Christian Corti wrote:
> The box was an imagination, but otherwise:
>
> "I am getting a very dim image even though the CRT itself appears to be in
> very good shape with no burn-in and otherwise crisp display. I think I've
> got a high-voltage problem[...]"
Yes, that;s what I remembered. Several of us said that if the image was
normal size, it was not a final-anode voltage problem (if that voltage
was low, the image would, indeed, be dim, but also much enlarged).
is in contradiction to this:
"In this case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. "
One statement was after the other. But usually, burn-in takes longer than
that.
7:53 a.m.
On Wednesday (12/04/2013 at 10:52AM +0100), Christian Corti wrote:
On Tue, 3 Dec 2013, Tony Duell wrote:
Then I must have mis-read, too. I thought he said that the terminal
was in its original box and had a pristine looking CRT.
No. Sorry guys. I meant that the video displayed was crisp and clear
but just dim. The tube clearly had burn-in, like an RT-11 DIR display
had been shown 24x7 for 15 years :-(
Nothing new in the box-- these came from a barn after salvage from
telephone central offices. They clearly served their time.
Only thing I have new in the box are a few replacement CRTs and so now having
proved there is nothing wrong with the electronics in this unit, it will get
one of the new CRTs.
Chris
--
Chris Elmquist
In this
case, the CRT also had a large amount of burn-in so was highly
suspecious due to that alone. The only thing I liked about it was
Oh, I must have mis-read what you said. I thought you sid the CRT looked
perfect.
2 Dec
2 Dec
2:01 p.m.
Have you measured the filament voltage to the CRT ?
not sure what
VT220s would be, but I IIRC on arcade stuff is is I think 6.3V.
VT220s (and all other VT's I've seen) are 12V or so (I've sene it quoted
as 11.5V).
Most of the time in mono montiros and terminals, a thin-neck CCRT with a
modifed B7G (7 pin) base has a 12V or so heater, a thicker neck CRT with
a P8H (8 pin with a central plastic locating key) base has a 6.3V heater.
Most colour CRTs hace 6.3V heaters.
-tony
1 Dec
1 Dec
5:04 p.m.
Hi Chris,
I remember 2 types of 220s, and have parts for at least one of them here. I
would need the part number also. I have most of the VT100, 101,etc logic
boards too.
Thanks, Paul
On Sun, Dec 1, 2013 at 2:26 PM, Chris Elmquist <chrise at pobox.com> wrote:
I recently "saved" a small pile of VT220 and
VT100 terminals from a
barn in western WI. They were grubby and have various issues but I am
enjoying cleaning them up and making a few good ones from some bad ones.
One of the VT220 is a very new vintage unit. Circa-1987, with some
components with date codes 1990. It has a totally different logic
board than earlier models I've worked on-- this one having a large PLCC
package in the center of the board which I assume is a custom device
integrating the video controller and much of the support logic since
there are considerably fewer parts on this board than the older ones.
Still an 8031 CPU though.
This unit also has a totally different video monitor circuit than the
older ones and my problem lies somewhere on that board-- I am getting
a very dim image even though the CRT itself appears to be in very good
shape with no burn-in and otherwise crisp display. I think I've got a
high-voltage problem but without schematics to match this board, it's
kind of a crap shoot to start debugging.
So, wondering if anyone has newer schematics or technical reference for
the VT220 than we find out on bitsavers? The bitsavers docs are circa-
1983 so I am looking for something 1987 or later when it appears they
did a considerable redesign of the guts of this terminal.
Chris
--
Chris Elmquist
2 Dec
2 Dec
7:08 a.m.
Hi Paul,
In this particular case, it was the CRT that was weak and so swapping
that resulted in success.
I'm pretty well set with other parts as well (although, we'll see when
I dig into the VT100s) but the schematics and/or technical reference
for the newer design VT220 might be the new quest. If you have any docs
stashed, would be great to get them scanned and out in the archives.
I'd be happy to take care of scanning if you do have them.
Chris
On Sunday (12/01/2013 at 07:04PM -0600), Paul Anderson wrote:
Hi Chris,
I remember 2 types of 220s, and have parts for at least one of them here. I
would need the part number also. I have most of the VT100, 101,etc logic
boards too.
Thanks, Paul
On Sun, Dec 1, 2013 at 2:26 PM, Chris Elmquist <chrise at pobox.com> wrote:
> I recently "saved" a small pile of VT220 and VT100 terminals from a
> barn in western WI. They were grubby and have various issues but I am
> enjoying cleaning them up and making a few good ones from some bad ones.
>
> One of the VT220 is a very new vintage unit. Circa-1987, with some
> components with date codes 1990. It has a totally different logic
> board than earlier models I've worked on-- this one having a large PLCC
> package in the center of the board which I assume is a custom device
> integrating the video controller and much of the support logic since
> there are considerably fewer parts on this board than the older ones.
> Still an 8031 CPU though.
>
> This unit also has a totally different video monitor circuit than the
> older ones and my problem lies somewhere on that board-- I am getting
> a very dim image even though the CRT itself appears to be in very good
> shape with no burn-in and otherwise crisp display. I think I've got a
> high-voltage problem but without schematics to match this board, it's
> kind of a crap shoot to start debugging.
>
> So, wondering if anyone has newer schematics or technical reference for
> the VT220 than we find out on bitsavers? The bitsavers docs are circa-
> 1983 so I am looking for something 1987 or later when it appears they
> did a considerable redesign of the guts of this terminal.
>
> Chris
> --
> Chris Elmquist
>
>
--
Chris Elmquist
10:26 a.m.
I agree. Dim is not a HV problem. It might be a voltage level problem
of the grids or cathode but often just poor emission of the cathode.
Some times one can get more life by running the filament at a higher
voltage for 10 mins or so. Usually 1.5 times or greater. Of course
this runs the risk of causing the filament to fail.
That is why one should ensure your getting good full swing of the
signal, first, and something upstream isn't limiting the contrast.
Dwight
Date: Sun, 1 Dec 2013 19:04:41 -0600
Subject: Re: Fix'n VT220s
From: useddec at gmail.com
To: cctalk at classiccmp.org
Hi Chris,
I remember 2 types of 220s, and have parts for at least one of them here. I
would need the part number also. I have most of the VT100, 101,etc logic
boards too.
Thanks, Paul
On Sun, Dec 1, 2013 at 2:26 PM, Chris Elmquist <chrise at pobox.com> wrote:
> I recently "saved" a small pile of VT220 and VT100 terminals from a
> barn in western WI. They were grubby and have various issues but I am
> enjoying cleaning them up and making a few good ones from some bad ones.
>
> One of the VT220 is a very new vintage unit. Circa-1987, with some
> components with date codes 1990. It has a totally different logic
> board than earlier models I've worked on-- this one having a large PLCC
> package in the center of the board which I assume is a custom device
> integrating the video controller and much of the support logic since
> there are considerably fewer parts on this board than the older ones.
> Still an 8031 CPU though.
>
> This unit also has a totally different video monitor circuit than the
> older ones and my problem lies somewhere on that board-- I am getting
> a very dim image even though the CRT itself appears to be in very good
> shape with no burn-in and otherwise crisp display. I think I've got a
> high-voltage problem but without schematics to match this board, it's
> kind of a crap shoot to start debugging.
>
> So, wondering if anyone has newer schematics or technical reference for
> the VT220 than we find out on bitsavers? The bitsavers docs are circa-
> 1983 so I am looking for something 1987 or later when it appears they
> did a considerable redesign of the guts of this terminal.
>
> Chris
> --
> Chris Elmquist
>
>
11:24 a.m.
New subject: VT525
Hi.
I am looking for a DEC VT525.
I know there is a second brand building a clone, Boundless Terminals.
I am looking for the original DEC.
I bought one on eBay but was not working.
If anyone wants to sell one, please tell me.
Inaki.
1:58 p.m.
This unit also has a totally different video monitor
circuit than the
older ones and my problem lies somewhere on that board-- I am getting
a very dim image even though the CRT itself appears to be in very good
I know nothing aobut this VT220, but I';ve worked on plenty of CRT-based
monitors....
My first question is : 'Is the picture approximately normal size (even
though it's dim) or is it much too large?'
The point being that if the EHT (HV, fianl andoe votlage) is low, the
picture will be dim, but it will also be large. The slower electrons are
easier to deflect (to put it over-simply).
If the picutre is abotu right for size, I would suspect one of the other
votlages. Maybe first anode (g2 to you). Maybe the control grid. You
could try comparing the CRT pin voltages with those in a workint unit to
see if one is way off.
I suppose it could be a low-emission CRT.
A 'silly' whihc I will admit caught me once, is a very dirty screen. Yes,
I spent a long time goign trhough the video PCB in a VT100 trying to find
a fault when the reason for a dim siplay was the screen was caked in dirt.
-tony
3803
days inactive
3807
days old
20 comments
9 participants
participants (9)
-
ard＠p850ug1.demon.co.uk -
cc＠informatik.uni-stuttgart.de -
chrise＠pobox.com -
cisin＠xenosoft.com -
contact＠xilcore.com -
dkelvey＠hotmail.com -
jules.richardson99＠gmail.com -
rescue＠hawkmountain.net -
useddec＠gmail.com