29 Jan
2024
29 Jan
'24
8:40 a.m.
A quick note on ADM3a screen rot... my vintage collection resides in a cool
(60-72 degrees F) dry basement. My "pride and joy" ADM3a (I have several)
was just starting to show a few bubbles at the corners last September. I
was pulling out some parts units on Friday and noticed that one had a much
better screen than I remembered. Thinking that I might swap screens, I took
a close look at "PnJ" and discovered to my horror that most of the lower
half of the screen had "melted". "PnJ" was on a shelf, below eye
level,
nowhere near a vent or other source of heat. I was so annoyed that I
immediately started cleaning/repair without taking any pictures (sorry).
Fortunately, there does not appear to be any corrosion from the "goo". I
completely desoldered and removed the keyboard assembly to get all of the
crud out of (and out from under) it. The mainboard is a fully socketed
example and the crud is down in several of the sockets. I'm still working
on that. Anyway, the take away is don't assume (like I did) that the ruined
ADM3as you see are the result of temperature extremes. It can happen
anywhere. Keep a close eye on yours if you have one.
Bill S.
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29 Jan
29 Jan
9:16 a.m.
Is there a definitive guide for repairing screen rot. One of mine needs
it. I have watched others but I have not attempted my own. I might try
this at the Kennett Classic workshop this upcoming Feb 17th
Bill
On Mon, Jan 29, 2024 at 11:41 AM William Sudbrink via cctalk <
cctalk(a)classiccmp.org> wrote:
A quick note on ADM3a screen rot... my vintage
collection resides in a cool
(60-72 degrees F) dry basement. My "pride and joy" ADM3a (I have several)
was just starting to show a few bubbles at the corners last September. I
was pulling out some parts units on Friday and noticed that one had a much
better screen than I remembered. Thinking that I might swap screens, I
took
a close look at "PnJ" and discovered to my horror that most of the lower
half of the screen had "melted". "PnJ" was on a shelf, below eye
level,
nowhere near a vent or other source of heat. I was so annoyed that I
immediately started cleaning/repair without taking any pictures (sorry).
Fortunately, there does not appear to be any corrosion from the "goo". I
completely desoldered and removed the keyboard assembly to get all of the
crud out of (and out from under) it. The mainboard is a fully socketed
example and the crud is down in several of the sockets. I'm still working
on that. Anyway, the take away is don't assume (like I did) that the
ruined
ADM3as you see are the result of temperature extremes. It can happen
anywhere. Keep a close eye on yours if you have one.
Bill S.
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9:54 a.m.
New subject: FW: Re: ADM3a screen rot.
There are several YT videos as you mentioned. Definitive is in the eye of the beholder, I
think. In hindsight, I would remind people to keep their cool and carefully think through
the safety procedures related to CRTs before starting any work. I totally forgot to
discharge my CRT but I got away with it (I guess because it had not been powered on for
four months). An interesting side note is that the anode cap on the leaking CRT had gone
rock hard and there was a small "streak" on the back of the CRT that looked like
the plastic that it was made of had released some sort of oil. Maybe it was attacked by
something outgassing from the goo that the CRT was dripping. Anyway, like Wile E Coyote,
after I had shoved a screwdriver under the uncooperative anode cap and finally gotten it
off, I suddenly thought "What the HE** did I just do???".
Bill S.
-----Original Message-----
From: Bill Degnan via cctalk [mailto:cctalk@classiccmp.org]
Sent: Monday, January 29, 2024 12:16 PM
To: General Discussion: On-Topic and Off-Topic Posts <cctalk(a)classiccmp.org>
Cc: Bill Degnan <billdegnan(a)gmail.com>
Subject: [cctalk] Re: ADM3a screen rot.
Is there a definitive guide for repairing screen rot. One of mine needs it. I have
watched others but I have not attempted my own. I might try this at the Kennett Classic
workshop this upcoming Feb 17th Bill
On Mon, Jan 29, 2024 at 11:41 AM William Sudbrink via cctalk <
cctalk(a)classiccmp.org> wrote:
A quick note on ADM3a screen rot... my vintage
collection resides in a
cool
(60-72 degrees F) dry basement. My "pride and joy" ADM3a (I have
several) was just starting to show a few bubbles at the corners last
September. I was pulling out some parts units on Friday and noticed
that one had a much better screen than I remembered. Thinking that I
might swap screens, I took a close look at "PnJ" and discovered to my
horror that most of the lower half of the screen had "melted".
"PnJ"
was on a shelf, below eye level, nowhere near a vent or other source
of heat. I was so annoyed that I immediately started cleaning/repair
without taking any pictures (sorry).
Fortunately, there does not appear to be any corrosion from the "goo".
I completely desoldered and removed the keyboard assembly to get all
of the crud out of (and out from under) it. The mainboard is a fully
socketed example and the crud is down in several of the sockets. I'm
still working on that. Anyway, the take away is don't assume (like I
did) that the ruined ADM3as you see are the result of temperature
extremes. It can happen anywhere. Keep a close eye on yours if you
have one.
Bill S.
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10:56 a.m.
On Jan 29, 2024, at 9:54 AM, William Sudbrink via
cctalk <cctalk(a)classiccmp.org> wrote:
...the anode cap on the leaking CRT had gone rock hard and there was a small
"streak" on the back of the CRT that looked like the plastic that it was made of
had released some sort of oil…
Often times dielectric grease is used around anode caps, and it’s not unusual to see
streaks like this. Usually harmless, but you can clean it up and replace/freshen it if
you replace the hardened rubber cap. Be careful with such cleaning on the tube, though —
depending on the tube, there may be an external aquadag coating which you won’t want to
damage/remove.
—FritzM.
noon
New subject: FW: Re: ADM3a screen rot.
On Mon, Jan 29, 2024 at 9:55 AM William Sudbrink via cctalk <
cctalk(a)classiccmp.org> wrote:
There are several YT videos as you mentioned.
Definitive is in the eye of
the beholder, I think. In hindsight, I would remind people to keep their
cool and carefully think through the safety procedures related to CRTs
before starting any work. I totally forgot to discharge my CRT but I got
away with it (I guess because it had not been powered on for four months).
An interesting side note is that the anode cap on the leaking CRT had gone
rock hard and there was a small "streak" on the back of the CRT that looked
like the plastic that it was made of had released some sort of oil. Maybe
it was attacked by something outgassing from the goo that the CRT was
dripping. Anyway, like Wile E Coyote, after I had shoved a screwdriver
under the uncooperative anode cap and finally gotten it off, I suddenly
thought "What the HE** did I just do???".
Bill S.
I think you were fine. That's how you discharge them anyway. You were
just missing the grounding wire :)
Sellam
-----Original Message-----
From: Bill Degnan via cctalk
[mailto:cctalk@classiccmp.org]
Sent: Monday, January 29, 2024 12:16 PM
To: General Discussion: On-Topic and Off-Topic Posts <
cctalk(a)classiccmp.org>
Cc: Bill Degnan <billdegnan(a)gmail.com>
Subject: [cctalk] Re: ADM3a screen rot.
Is there a definitive guide for repairing screen rot. One of mine needs
it. I have watched others but I have not attempted my own. I might try
this at the Kennett Classic workshop this upcoming Feb 17th Bill
On Mon, Jan 29, 2024 at 11:41 AM William Sudbrink via cctalk <
cctalk(a)classiccmp.org> wrote:
A quick note on ADM3a screen rot... my vintage
collection resides in a
cool
(60-72 degrees F) dry basement. My "pride and joy" ADM3a (I have
several) was just starting to show a few bubbles at the corners last
September. I was pulling out some parts units on Friday and noticed
that one had a much better screen than I remembered. Thinking that I
might swap screens, I took a close look at "PnJ" and discovered to my
horror that most of the lower half of the screen had "melted".
"PnJ"
was on a shelf, below eye level, nowhere near a vent or other source
of heat. I was so annoyed that I immediately started cleaning/repair
without taking any pictures (sorry).
Fortunately, there does not appear to be any corrosion from the "goo".
I completely desoldered and removed the keyboard assembly to get all
of the crud out of (and out from under) it. The mainboard is a fully
socketed example and the crud is down in several of the sockets. I'm
still working on that. Anyway, the take away is don't assume (like I
did) that the ruined ADM3as you see are the result of temperature
extremes. It can happen anywhere. Keep a close eye on yours if you
have one.
Bill S.
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12:05 p.m.
New subject: FW: Re: ADM3a screen rot.
On 01/29/2024 2:00 PM CST Sellam Abraham via cctalk
<cctalk(a)classiccmp.org> wrote:
On Mon, Jan 29, 2024 at 9:55 AM William Sudbrink via cctalk <
cctalk(a)classiccmp.org> wrote:
dripping.
Anyway, like Wile E Coyote, after I had shoved a screwdriver
under the uncooperative anode cap and finally gotten it off, I suddenly
thought "What the HE** did I just do???".
Bill S.
I think you were fine. That's how you discharge them anyway. You were
just missing the grounding wire :)
Sellam
12:45 p.m.
New subject: FW: Re: ADM3a screen rot.
Sellam Abraham wrote:
I think you were fine. That's how you discharge
them anyway. You were just missing the grounding wire :)
Yes, I have one set up for just that purpose. Wire clamped to the shaft with an alligator
at the other end.
But I was so pissed off, I just grabbed a screwdriver off of my workbench. I'd rather
not be the electron sink
In this case. I've never taken a hit off of a CRT have you?
Bill S.
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3:59 p.m.
New subject: FW: Re: ADM3a screen rot.
On 29/01/2024 20:45, William Sudbrink via cctalk wrote:
Sellam Abraham wrote:
> I think you were fine. That's how you discharge them anyway. You
> were just missing the grounding wire :)
I'd rather not be the electron sink In this case.
I've never taken a
hit off of a CRT have you?
Yes, from a 26" CRT in a colour TV. It threw me across the room and
taught me a lesson I'll not forget.
BTW, if anyone has CRTs lying out of circuit, don't assume they're safe
either. The EHT in normal use forces electrons into the glass, and when
disconnected they very slowly migrate back to the aquadag, producing a
substantial voltage. I remember seeing this demonstrated on an
electronics course several decades ago. Which is where I /should/ have
learned about discharging CRTs *through a suitable resistor* :-)
--
Pete
Pete Turnbull
4:34 p.m.
On Jan 29, 2024, at 6:59 PM, Pete Turnbull via cctalk
<cctalk(a)classiccmp.org> wrote:
On 29/01/2024 20:45, William Sudbrink via cctalk wrote:
This apparently is true of some capacitors as well, I'm not sure which types.
paul
Sellam Abraham wrote:
> I think you were fine. That's how you discharge them anyway. You
> were just missing the grounding wire :)
I'd rather not be the electron sink In this
case. I've never taken a
hit off of a CRT have you?
Yes, from a 26" CRT in a colour TV. It threw me across the room and
taught me a lesson I'll not forget.
BTW, if anyone has CRTs lying out of circuit, don't assume they're safe
either. The EHT in normal use forces electrons into the glass, and when
disconnected they very slowly migrate back to the aquadag, producing a
substantial voltage. I remember seeing this demonstrated on an
electronics course several decades ago. Which is where I /should/ have
learned about discharging CRTs *through a suitable resistor* :-) 
5:47 p.m.
This apparently is true of some capacitors as well,
I'm not sure which types.
It is true of all capacitors (CRTs are intentional capacitors, after all) designed for and
subjected to sufficiently high voltage. It's referred to as dielectric absorption, and
is why HV caps ship from the factory with the leads shorted.
I have a 4.7 uF tens-of-kV capacitor in the shop for reasons. The shorting jumper got
knocked off once while moving stuff past it, and I noticed it the next day. By that point,
it had accumulated enough charge to register over 200V on a Simpson 260 VOM (not a high
impedance meter). I don't know if that was accumulated static charge or from
dielectric absorption.
Thanks,
Jonathan
5:56 p.m.
On Jan 29, 2024, at 8:47 PM, Jonathan Chapman via
cctalk <cctalk(a)classiccmp.org> wrote:
Thanks for the confirmation. And also a good reminder that static electricity is one way
to charge capacitors, at least ones with good dielectrics. After all, the famous Leyden
jar is nothing more than a capacitor charged by static electricity, and it can certainly
hand out substantial shocks.
paul
This apparently is true of some capacitors as
well, I'm not sure which types.
It is true of all capacitors (CRTs are intentional capacitors, after all) designed for
and subjected to sufficiently high voltage. It's referred to as dielectric absorption,
and is why HV caps ship from the factory with the leads shorted.
I have a 4.7 uF tens-of-kV capacitor in the shop for reasons. The shorting jumper got
knocked off once while moving stuff past it, and I noticed it the next day. By that point,
it had accumulated enough charge to register over 200V on a Simpson 260 VOM (not a high
impedance meter). I don't know if that was accumulated static charge or from
dielectric absorption.
Thanks,
Jonathan 
10:43 p.m.
New subject: FW: Re: ADM3a screen rot.
On 2024/01/29 12:45 p.m., William Sudbrink via cctalk wrote:
Sellam Abraham wrote:
I had a chat with an electrical engineer about discharging old picture
tubes many years ago, and he highly recommended using a suitable
resistor array - like a HV probe to drain the charge on B&W monitors.
Particularly ones that had a separate HV diode. He told me that
discharging with a screwdriver can pass too much current (caused by a
cascade of charges) through the diode array and damage them.
This explained a problem we were having with B&W XY monitors made by
Electrohome and Wells Gardner where the diode that was mounted between
the HV transformer and the picture tube would fail and run hot, over
heating the silicon rubber caps on the ends. I've not lost any HV diodes
on machines since using our HV probe to discharge since that time.
John :-#)#
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Call (604)872-5757 (Pinballs, Jukes, Video Games)
flippers.com
"Old pinballers never die, they just flip out"
I think you were fine. That's how you
discharge them anyway. You were just missing the grounding wire :)
Yes, I have one
set up for just that purpose. Wire clamped to the shaft with an alligator at the other
end.
But I was so pissed off, I just grabbed a screwdriver off of my workbench. I'd
rather not be the electron sink
In this case. I've never taken a hit off of a CRT have you?
Bill S.
331
days inactive
332
days old
11 comments
9 participants
participants (9)
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Bill Degnan -
Fritz Mueller -
John Robertson -
Jonathan Chapman -
Paul Koning -
Pete Turnbull -
Sellam Abraham -
William Sudbrink -
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