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Toshiba T5200 plasma problem

kerr

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Oct 21, 2021
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Melbourne, Australia
Hi all , this is a long shot but short of buying a new T5200, I'm kinda stumped ‍♂️

Basically the display doesn't work properly anymore. All pixels work, but instead of the black background, it's an orange on orange. Anyways a pic says 1000 words.

I've stripped the machine of HDD, FDD, VGA card, KB, with no change. Note that external video is not affected.

PSU appears to be giving out the right juice ⚡. I've even tried another PSU. Also tried different RAM.

Have re-seated everything and cracked open the display but nothing obvious.

Hoping someone's seen this before or knows where I should look..

I would be happy to put a bounty on this if someone can help!

Thanks!
 

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GiGaBiTe

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Not really familiar with gas plasma displays, but have you checked the capacitors? Old failing capacitors are one of the biggest problems with old computers.

I'm not sure if the screen has capacitors inside of it, but if external video is working fine, I'd suspect bad capacitors in the screen itself, or the circuitry driving the screen. The original Powerbooks are notorious for screen failure due to leaking capacitors inside the screen assembly. It's not a fun job having to change them out.
 

NeXT

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Hmm. I know what you are saying. I have a 5200sx which has that amazing high contrast plasma but I have not seen mine do that. It looks very similar now to the plasma display on a compaq portable III/386 where the bachground is always a lit orange. I wonder if its something like an intensity bit isn't making its way to the screen controller or a contrast issue.
 

eswan

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Stupid question, but it has to be asked. You have fiddled with the brightness knob? Did it have any effect?
Maybe try a cmos reset by unplugging the battery?
I don't know if these had a utility to change the pallet, some monochrome systems did to try to emulate color differences better.
I've got the pinout somewhere, but it's pretty simple. 4 bits greyscale, horizontal clock, vertical clock, display enable, gnd. Should be able to check for a stuck bit with an o'scope or a logic probe.
 

GiGaBiTe

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No - I haven't. But yes, there are caps on the rear of the PDP and on the converter board. These are easy to access and I have an ESR meter and multimeter so let me give that a crack, thanks!

Make sure they're out of circuit when you test them, or you'll get incorrect readings. A multimeter won't really do any good unless it can read capacitance, not all of them can, and the ones that do often can't read over something silly like 10-100 uF, which makes them not very useful.

Assuming there's nothing physically wrong with the capacitors, in addition to ESR, you need to check for electrical leakage. Since most people don't have a leakage tester, you can often gauge leakage from the capacitance value read. If you get a capacitance value outside of the +/-20% range, you can be sure there's leakage and the capacitor needs to go. So, if you have a 47 uF cap that's reading 100 uF, it's not an over achiever, it's bad.
 

soviet9922

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Used to have a brightness issue on a t3200sx, recapping the display and the power supply fixed the brightness issue I have a thread about it here:https://www.vcfed.org/forum/forum/g...32-have-a-bizarre-issue-on-my-t3200sx-display

But your issue is not sure if is the same your display looks more like the one from the Compaq 386 and a generic portable that I have. The background looks orange and I hate it recapping these systems doesn't "fix" this also there's a pot on the back of the display that does something to the brightness adjusting it could get this a little better.

The best could be to recap the system to be sure.
 

kerr

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Thanks for the ideas, I'll try re-capping. Have tried disconnecting the contrast wheel entirely with no improvement. The wheel does work and changes the screen brightness but doesn't fix the issue.

Will keep you posted.
 

kerr

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Hi all, at this stage the problem has beaten me. I did a whole bunch of capacitor testing and continuity tested at least half of the wiring harness, all the way to the PDP plug.

I noticed that it's the screen background that's showing as light orange instead of black (pixels off) in both text mode and graphics mode, same thing. Therefore I'm wondering if a GND connector is the issue.

The display/VGA card has also got some acid damage (guessing a full length ISA SCSI/RAID card had a battery that leaked at some stage). The connections test OK though.

I'm gonna leave it for now - I'd really need another screen/VGA card to test with and rule out some variables.
 

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Niezgodka

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I have the same problem with T3200SXC color display :(
I consider replacing it with suitable vga display. Can somebody recommend any?
 

Hugo Holden

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I would think this would be a straightforward problem to fault find.

It would require the schematic of the VDU/display, a working theory on how the display worked and a good scope, to look at the display drive signals to check if it was the signals themselves that were abnormal, resulting in the display faithfully following them, or if it was a case of correct signals and an abnormal display issue/fault.

A lot of the time, suggestions about faulty caps can be a shot in the dark. Because this is just a shotgun approach to diagnosis & repair. A targeted approach is much better, with a lot less collateral damage too. There is no substitute for having the documentation and performing checks with a scope, to get to the bottom of a fault.
 

kerr

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Hey all, I'm still no further ahead unfortunately :confused:

Unfortunately I don't have the schematics or a scope (or the knowledge to use one).

I can see some acid damage/spill on the graphics card (if it quacks like a duck...), so I'll try tracking down a replacement 🙏

I did a bunch of basic continuity tests on the PCB traces and that seemed OK, so a replacement may not fix it, but gotta try, right?

FWIW, here's a pic, of the board:

AM-JKLUAmCnj5HeXRolyVGmLMjKGSeUsI8VL-hI1mxYeH0tiVx1yNcOqcqlvo4m2H7boIZWHPACZINb1K9-BNhsYGCcfo8uyqG3veHUjqPn5mtWAcR4894eqjQcQxc6kKUamLMMNGi3bwi-Q0FHVdW-n3oNdGA=w1310-h874-no
 

twolazy

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Upside that should be a 2 layer pcb, so shouldnt be too hard to repair. I try cleaning it up with some windex and brush, and see what you get... worse case a few bodge wires. Middle left looks like the pulldown resistors for the brightness, I would start there...

I'll have a non posting t5300 soon, and since the models are similar perhaps I can help with readings. I dont see the video card being much different.

BTW, on topic of the psu, are you just using a modern 19v?
 
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GiGaBiTe

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FWIW, here's a pic, of the board

You have quite a number of damaged traces, solder joints and potentially VIAs. You don't need a scope to fix those.

It looks fixable, depending on whether ICs on the other side of the board were also damaged.
 

twolazy

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If you havent already, pull that nicad/nimh battery quick. Its most likely what is gassing out and corroding the inside.
 

twolazy

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WD40 is great for corrosion as well, just keep in mind it will be bare copper traces after, so will need to use some nail polish.
 

twolazy

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Man I feel like a goofball, I totally brainfarted, and have a Compaq on the way (t5300) not Toshiba. Doh! Getting older stinks! LoL
 
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