VOGONS


First post, by Jonas-fr

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Hi got the strangest issue with a GD610/620 based ISA video card (Stingray Rev4+, more info on it) on a 486 system. The video is ok in the embedded monochrome LCD (dedicated connector on the card) but as soon as the POST is finished and then the screen change (to show the HDD booting or in my case a message showing that no HDD is present) the screen is fully garbled. We can discernate some of the displayed text-UI features and shapes but it's hardly useable.

FWIW I'v got this issue right after dumping the BIOS of the card from a TL866 while using ESD safe tools.

What I've tried so far (without any success):
- cleaning the ISA card's gold connectors with IPA and paper (they were ok)
- removing all cards from the mobo if not the VGA card
- reseating both the BIOS chip and the RAMDAC on the video card
- putting the card on another ISA port
- trying enabling all the shadow memory option (despair mode activated)

Video of the issue :
https://streamable.com/6lrgrv

Pic of the garbled screen :
TSGe

Pics of the BIOS config (same as when the computer worked) :

uFnI

ZNvI

What I haven't tried:
- using it on external VGA (since switching from the internal LCD to the external VGA needs entering a command it's not exactly practical with a garbled screen !)
- replacing capacitors (they are small yellow ones and they all look pretty much ok)
- using the card on another mobo (the internal LCD wiring harness isn't long enough, so short of dismantling all the LCD assembly it isn't an easy test to do)

Last edited by Stiletto on 2020-08-11, 01:06. Edited 2 times in total.

Reply 1 of 7, by Jonas-fr

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I made a minimalist DOS bootdisk with switch.com TSR utility and with a stroke of CTRL-SHIFT-D I noticed that the video output on the external VGA display was good so it's definitively an issue regarding the circuit dedicated for the embedded LCD on the card which is the culprit (bad memory, bad trace and/or bad capacitor). Since the card is looking ok I think I'll change the capacitor. Ideally I'd like to use the same type as the ones on the card (little yellow blobs) but not sure what type they are, here's a pic of it (56K warning)
https://www.mirari.fr/FkOr

Anybody recognise them ? Can I still found the same type today of another modern replacement should be used? I'd rather use through hole components where possible but can do with SMD since I've got the tools and that the small pitch of the current caps would be perfect for SMD stuff here.

Last edited by Jonas-fr on 2020-07-22, 07:25. Edited 1 time in total.

Reply 3 of 7, by Jonas-fr

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Does anyone encountered graphical issues/glitches while switching between video modes on a ISA graphic card (especially at boot)? It might give me a hint of what's going on. If anyone knows a testing program that switch video modes on demand that could help me doing a diagnostic here.

Reply 4 of 7, by Jonas-fr

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If it can help graphical mode is ok : I blindly started Doom and up until the initialisation (text mode) it's garbled but upon the appearance of the title screen (graphic almode) all is good. I begin to think that maybe the BIOS ROM might be slightly corrupted, at least on the code page level/selection code?

Reply 5 of 7, by shamino

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Jonas-fr wrote on 2020-07-21, 16:44:

Since the card is looking ok I think I'll change the capacitor. Ideally I'd like to use the same type as the ones on the card (little yellow blobs) but not sure what type they are, here's a pic of it (56K warning)
https://www.mirari.fr/FkOr

Anybody recognise them ? Can I still found the same type today of another modern replacement should be used? I'd rather use through hole components where possible but can do with SMD since I've got the tools and that the small pitch of the current caps would be perfect for SMD stuff here.

Do you see any kind of polarity marking on them?
If not, they might be ceramic caps. Ceramic caps are chill and don't have polarity.
If they do have polarity markings then they're probably tantalums. Tantalums are violently polar, like American politics.

Tantalums (at least the ones I've seen) mark the *positive* side, not the negative. To confirm how they're marked you could probe for continuity against known GND or positive voltage points. I should add the caveat that there could be negative voltage rails involved, in which case GND would be on the positive side of the cap. I've hardly ever encountered that but I've never worked on a computer this old.

If they have numbers printed on them, it's probably indicating their value in picoFarads.

I think the chance of ceramic or tantalum caps failing is pretty low, and if tantalums fail you usually know it (they like to explode when they get mad, thus nicknamed "tantrum" caps).

Reply 6 of 7, by Jo22

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This is perhaps not what you're looking for, but I know that the Japanese version of DOS 6.20 (DOS/V 6.20) uses graphics mode to display Kanji.
Maybe it is useful for testing thus (English mode uses native text mode).
You can switch between modes by typing "us"and "jp" , if memory serves.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 7 of 7, by Jonas-fr

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Thanks shamino and Jo22, I'll keep that in mind. i'm now focused on flashing a new video BIOS to see if that's not a BIOS issue. I'll test with the BIOS from this page (http://www.vgamuseum.info/index.php/cpu/item/ … -cl-gd610-620-c) and maybe matze79 will release its VGA BIOS from his/her card (Re: Help fixing rare CL-GD610/620 VGA card)