Gas Plasma Display repair

[CompaqSniffer]

Hello, I'm relatively new to the forum, however I think I can contribute quite a lot of knowledge of repairing Gas Plasma Displays. This knowledge was gained by experimenting/attempting to repair a gas plasma display for a Compaq Portable III. This knowledge can also be used for repairing Toshiba T3100 Gas plasma displays, which are the screens I cannibalized to repair the PIII screens.

I'm writing up a document on the repair process (WIP) just thought I would go ahead and post a link for a google document on my findings:

COMPAQ PIII / general Gas Plasma display Repair

Still Mostly A work in progress ABSTRACT This document is meant to catalogue the problems/ solutions I have encountered with Compaq portable III gas plasma displays. This document also catalogues a general idea of how these screens work to better understand how to repair them. SOURCESGene...

docs.google.com

Feel free to comment on the document, I'll post an excel file (google sheets) later to organize suggestions/ edits to add to the document, or you could do that yourself.

 

[djg]

Is document just the intro currently or am I not figuring out how to go to page with content? If just started can you post again when its ready to read? I have one with a few intermittent columns.

 

[CompaqSniffer]

Yeah I'm just starting on w

Is document just the intro currently or am I not figuring out how to go to page with content? If just started can you post again when its ready to read? I have one with a few intermittent columns.

yeah I'm just starting on writing it, I'll reply again when it's done, or most of it, I'm in class right now, so I probably won't work on the brunt of it until tonight. Yours shouldn't be too hard to fix, I'll go ahead and give you some info, you can narrow down which row of chips by unplugging the top or bottom row of chips. The top row controls odd, the bottom row even. Unplugging the top turns off the odd columns, and unplugging the bottom turns off the even columns. For example: if you unplug the top, turn on the screen, and there's a big dead spot instead of a dead line every even line then there's a bad chip on the bottom. also works if there's full bright lines(spoiler they are internal shorts). Unplugging the rows of chips one at a time really helps to narrow it down.

I'll explain in greater detail in the document and post pictures.

 

[joeventura]

Nice work thus far!!

 

[CloudInMyHead]

Any progresss?

 

[CompaqSniffer]

Any progresss?

Sadly not much, I'm going to be brutally honest, the ones that are worth the effort are screens that only have a few dead lines, or one dead IC. I keep running into this issue where I replace all of the bad ICs, and these vertical flickering lines start showing up:


I think they're caused by the resistor networks (white ceramic packages) that are only on the vertical sides:




Alot of them have that wierd white residue on them, which makes me think their the culprit for all of the noise. It could also be the panel itself. I tried practicing replacing one on a parts screen, and they're borderline impossible to get back on. One thing of note is that the screens with aluminum frames haven't shown any white residue or noise in The vertical.

I'm not really going to pursue repairs anymore, I'm getting really busy with college again. I want to focus more on figuring out how to retrofit an lcd or oled panel on using the internal proprietary connector. I think it's a weird cga or VGA connector, half of all the pins are ground.

one big positive thing is that if you only have a few dead lines in one spot, it's definitely worth repairs. Screens with several dead lines take a long time to fix. I'll edit up my guide here soon, if anyone else wants to take a crack at documenting repairs, I'll give you editing access. I think I've come to realize this might take several people documenting their version of plasma screens, and comparing common faults on them.

If you have an Oki electronics screen that still comes on, don't lose hope, from my experience, all the ones I've worked on were panel dead, or the ribbon cables were too far gone. None of them ever had vertical line flickering problems.

 

[CloudInMyHead]

I have to say you did a lot of great work here. I don't know enough to carry on, but I feel I now know enough to try fixing one of mine.

I have two bad displays. One is just about 1 letter's length vertical of wiggle which is readable but a little rough. The other is readable but many vertically lines. I didn't photograph either, but I should have as I was playing with my 4 Compaq IIIs today.

 

[CompaqSniffer]

I have to say you did a lot of great work here. I don't know enough to carry on, but I feel I now know enough to try fixing one of mine.

I have two bad displays. One is just about 1 letter's length vertical of wiggle which is readable but a little rough. The other is readable but many vertically lines. I didn't photograph either, but I should have as I was playing with my 4 Compaq IIIs today.

Do you have pictures of each? I could tell you if they have the possibility of the vertical flickering issue, and if they are worth the repairs. It seems that the ones with plastic frames grow weird white residue under their resistor networks causing the vertical line noise, but I haven't quite narrowed it down yet.
It could also be due to moisture and it only happens to the screens I have, since I live in SC and the apartment complex I live in has really high humidity. If you blast the resistor networks with a heat gun while the screen is on, the vertical flickering lines go away for a few seconds.

Not that you'll definitely have this issue, but that's something to watch out for.

 

[CloudInMyHead]

OK. This is one of my bad displays. Probably the worst one I have.
Funny thing is, this one would not boot up the other day. No matter which of my diagnostics disks I used, it wasn't having any of it. I lubed and clean the drive but to no avail. Weird though, today it was happy as a bee reading the diagnostics floppy. Anyway, this is one of two that are 286s. I have not removed the displays ever, hopefully its not too hard as I need to swap the two good ones I have to the two 386 Compaq IIIs. Ultimately, I want them all to be usable and then let both 286s go (likely). I love em all but I have too many orphans already.

Here are the display shots.

 

[CompaqSniffer]

OK. This is one of my bad displays. Probably the worst one I have.
Funny thing is, this one would not boot up the other day. No matter which of my diagnostics disks I used, it wasn't having any of it. I lubed and clean the drive but to no avail. Weird though, today it was happy as a bee reading the diagnostics floppy. Anyway, this is one of two that are 286s. I have not removed the displays ever, hopefully its not too hard as I need to swap the two good ones I have to the two 386 Compaq IIIs. Ultimately, I want them all to be usable and then let both 286s go (likely). I love em all but I have too many orphans already.

Here are the display shots.
View attachment 1307431

View attachment 1307432

Are those vertical lines intermittent? Like do they show up for a second then go away, or flickering? This was the issue I was talking about that I'm running into with mine. So far I haven't been able to fix it, but I think it has to do with the resistor networks. It's not caused by any bad ICs, I replaced all of the ICs on one screen and it was still having the problem.

 

[CloudInMyHead]

I'd say they don't flicker and depending on what's displayed there may be more or less vertical lines.

 

[CompaqSniffer]

I'd say they don't flicker and depending on what's displayed there may be more or less vertical lines.
View attachment 1307448

That's somewhat similar to the problem I was facing, I had that exact symptom too, but it was also sporadic and random when and where the lines would show up.

If you do take it apart, do your resistor networks also have this white residue?
This is the resistornetwork:

This is what the undersides of a lot of them look like for me:

Here's what it should look like on the underside from what I have found(ignore the solder):


You can look at the undersides by lifting up the flaps on the top and bottom sides of the screen. BE CAREFUL as they are of course glued down. I used a spudger and pried up inch by inch all along the side until it came up. The glue isn't strong, it's more like a piece of foam with both sides being sticky.

My hypothesis is that something is breaking down on these resistor networks, and shorting both sides to make a path that's lower in resistance. This bright line behavior I have mimicked by bridging the gap with just wire, and it causes similar artifacts.

I have had several theories leading up to this point about what the problem is, some included: breakdown of glue holding the resistor networks in place, moisture being trapped inside of them, and now I believe it might be a similar condition to vinegar syndrome, that green film on top of the networks might be breaking down and becoming conductive. Vinegar syndrome isn't what this is, but the premise is the same. with vinegar syndrome, the polarizer on lcds breaks down causing these wierd welts that form on the screen that smell like vinegar.

Fore these resistor networks, they don't have vinegar syndrome l, but I think it's having a similar problem where the protective film is breaking down because it's made of organic materials.

I have spent months on these screens, but no theory has stuck yet. I would need to do some more testing to find out what the actual issue is.

 

[CompaqSniffer]

I'd say they don't flicker and depending on what's displayed there may be more or less vertical lines.
View attachment 1307448

Do your resistor networks look like this?




I finally figured it out, that green film is breaking down, and the breakdown of it is conductive. Now, we have to figure out how to easily get that green film off. I think the only easy way to get it off would be chemically, however I don't even have the slightest clue how to do that. Maybe penetrative oil? Would anyone know how to get this green film off without damaging the traces and resistors underneath?

 

[CloudInMyHead]

To be honest....I got sidetracked with a Samsung Notebook 386. I have to go back and look. I powered on a 286 CP3 and it's display was perfect, so I need to swap the two displays completely. I was thinking of removing the entire display pop out as a complete section if that's possible. Then my 386 one will be good enough to use and I can focus on repairing the 286 CP3 display.

 

[CompaqSniffer]

Yeah, the screens are pretty interchangeable between models. I've been spending months trying to diagnose the exact problem you're facing, and now that I've fully figured it out, I'm kinda clueless on how to actually fix it. Those resistor networks have been the bane of my existence since Christmas. The ICs are well within reason to replace if you're good with a hot air gun, and can solder ICs with an iron, however, finding a fix for these resistor networks is going to be hard. I have to figure out a way to get that green film off, then find some other protective film that won't deteriorate on me. BTW that white residue, from a few hours of research, it is most likely some sort of salt compound. Not like table salt, but like the corrosion crystals you see on battery terminals. Also, it reeks of piss, which probably means it's decaying into ammonia as well. I'm thinking of dubbing this decaying phenomenon "piss syndrome", kinda like how LCDs can get "vinegar syndrome" from their polarizers decaying into acetic acid.

Truly an awful name for an awful affliction. If you take it apart, and the screen has a faint musty smell, you'll most likely have those decaying resistor networks.