Gas Plasma Display repair

[djg]

I took a picture of my old phone screen to show that it actually showed up in the list of things

That showed May 2025 so the document I linked to should be it.

 

[CompaqSniffer]

That showed May 2025 so the document I linked to should be it.

Thank you so much, I will re-upload this and save a backup.

From my most recent work, it seems after replacing the ICs, the screen never really goes back to normal. The white rectangles underneath the vertical section (the resistor networks) seem to be deteriorating. Like they literally look like the protective film on top is being eaten away at, and the whole thing smells of ammonia. I don't know if there is a way to replace these at all. I tried with a broken screen to practice transplanting one of the networks, but since the place I'm soldering to is flexible, and the pads are underneath of the networks, it is literally impossible to transplant a working one. The only way I can think of repairing these things is to take a knife and cut the traces, and individually solder through hole resistors across the gap.

OR, I have been wanting to learn PCB design, I or someone else may be able to design a PCB with pins that jut out of the sides that have SMD resistors on them. That would make it so that it is possible to use a soldering iron to individually solder each pin to the flex cable. However, getting the old network off without trouble and without ripping traces is nearly impossible since on the Matsushita ones, they are glued down. You could only really easily do it if you have an Oki branded one, and even then, it wouldn't be necessary since the Oki ones don't have the resistor network issue.

I'll attach what this deterioration looks like.

Normal one from an Oki screen for reference:


deteriorated ones:

 

[CompaqSniffer]

https://docs.google.com/document/d/1G5kzYG3R9cfRKe2dvm1y4UO2ySsCt9Yst409pRgTJsE/edit?usp=sharing

I'll edit some important info tomorrow if I have time, and I'll also have to fix the formatting. I don't like how I worded some of the sections in there so I'll go back and see if I can't fix them up.

Thank you so much djg!!!

 

[djg]

Think I finally got it. The white is likely ceramic that the resistors and traces are deposited on and then the green film was put on to protect it. Similar to the old hybrids. Is there enough power dissipation that the white gets warm during operation?

 

[CompaqSniffer]

Think I finally got it. The white is likely ceramic that the resistors and traces are deposited on and then the green film was put on to protect it. Similar to the old hybrids. Is there enough power dissipation that the white gets warm during operation?

Yes, I read up on it, this is specifically what they do for thick film resistors. They use the ceramic "tiles" as substrates to deposit the resistor films onto.

The resistor networks don't really get warm, it's mostly just the line driver ICs. I think there's something chemical going on to deteriorate the green protective film on the resistor networks. Maybe the bonding agent is decomposing, or the plasma discharge has some sort of effect on the surrounding electronics that speeds up deteriorating. I don't really know for sure.

 

[Istarian]

I would guess that the smell is in fact ammonia gas from degradation of the adhesive (possibly some kind of EVA glue) used to hold the resistor carrier to the flexible cabling.

It might also be a leftover from manufacturing processes or a byproduct of some sort of chemical reaction.

Hopefully you're working on this is a relatively well ventilated area... Sufficiently concentrated gaseous ammonia in can cause significant irritation to the eyes and respiratory tract.

Damage to other components or material from exposure to ammonia seems plausible.

 

[CompaqSniffer]

I would guess that the smell is in fact ammonia gas from degradation of the adhesive (possibly some kind of EVA glue) used to hold the resistor carrier to the flexible cabling.

It might also be a leftover from manufacturing processes or a byproduct of some sort of chemical reaction.

Hopefully you're working on this is a relatively well ventilated area... Sufficiently concentrated gaseous ammonia in can cause significant irritation to the eyes and respiratory tract.

Damage to other components or material from exposure to ammonia seems plausible.

Yeah I haven't done any real soldering on these in a while. Ammonia smell really sells it short, it smells more like soiled diapers. It is genuinely a terrible smell. I also recommend working on them in a well ventilated area because the smell can be somewhat gross.

 

[Istarian]

Unsurprisingly, a soiled diaper smells like that because it contains a mixture of urine and human feces...

Urine contains concentrated urea which has the chemical formula CO(NH2)2 and is converted by an enzyme into Ammonia and Carbon Dioxide.

The solid waste is partially decomposed organic matter which likely continues to decompose under the action of bacteria and enzymes after leaving the body.

 

[Radix]

Just a thought on the white residue - on DEC PDP-11 systems around 40+ years old, I have seen a number of systems with a white-ish corrosion on metal chassis, adjacent to self-adhesive foam - not under it - always next to it, where it seems to have attached the plated chassis material quite effectively... Our consensus was that it was probably/possibly the foam breaking down and releasing some of the nasty solvents used to make foam and a chemist in the current PU-foam industry agreed this was possible. No tests were dome to confirm, but the chemicals and residue may not be harmless of course!

Robin