VOGONS


First post, by Albercik

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Hello All,

Yesterday, I've built a new 486 PC. I have a bunch of ISA GPU's to be tested and one of them is Trident GPU with Trident TVGA8900C chip.

The card is giving an output to the screen and in DOS everything seems to be fine. Even in Norton Commander (with blue background) the GPU seems to be working fine. But... When running Windows 3.1 - there's snowing and gaussian-like effect (it looks like a low-res photo of a LCD screen,but it's moving) on the screen. When playing eg. Lotus III - there are vertical bars on the screen.

At the beggining I'd thought it's a faulty VGA cable, but I've replaced it still the same issue. Then I've swapped a card's memory taken from another (that's dead), and still nothing. After replacing the card with different GPU - the issue is gone.

Because those card's are quite rare and hard to find (at least here, in Poland) - I'd really love to save as many of them as it's possible.

Any thoughts on what may be causing the issue?

Here's the photo of the same card as mine:
?u=http%3A%2F%2Fwww.amoretro.de%2Fwp-content%2Fuploads%2Ftrident_tvga8900c_isa_tvga_isa.jpg&f=1&nofb=1

The only difference is that mine has blue capacitors. And this is my first thought - to replace the capacitors, but... I have no idea what are their values (capacity) as they have nothing written on them. I'm guessing - they're tantalum caps, but I'm not sure if I can replace them with an ordinary, electrolythic caps.

Any help will be much appreciated!

[EDIT] Found some markings on the capacitors - the bigger ones are 10u 16V and the smaller ones are 2+2 16V tantalum. Before I'll start playing with soldering iron - can you please confirm if I'm thinking correctly that this issue can be cause by faulty capacitors?

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 2 of 7, by Albercik

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Ydee wrote on 2021-10-25, 09:18:

Thanks for the link, but I've already read this topic. However, they say that some of the cards will have a problem with LCD screen. In my case - after replacing the VGA card with the very same (I mean identical) model - the issue is gone (I have three of those cards). After testing another set of cards - there's no issue with CirrusLogic GD5320. I have two Tridents TVGA9000B and the issue exists with one of them, and not with the second one.

That's why I'd thought of capacitors in a first place...

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 3 of 7, by zyga64

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Yes, you can replace tantalum capacitors with ordinary electrolytic. It's worth to try just to eliminate one of the possibilities.
It is always a good idea to check the quality of the supply voltage (if you have access to osciloscope).

Among early motherboards, they sometimes suffer from ISA bus noise. https://www.smbaker.com/diagnosing-xi-8088-stability-issues
This is why various cards work unstably (I suspect this may be the cause of the instability of 1st gen. Aztech soundcard on my 286 VLSI SCAMP board),
but I assume that your 486 is mature enough. Some cards are simply more sensitive to noise/interference.

1) VLSI SCAMP /286@20 /4M /CL-GD5422 /CMI8330
2) i420EX /486DX33 /16M /TGUI9440 /GUS+ALS100+MT32PI
3) i430FX /K6-2@400 /64M /Rage Pro PCI /ES1370+YMF718
4) i440BX /P!!!750 /256M /MX440 /SBLive!
5) iB75 /3470s /4G /HD7750 /HDA

Reply 4 of 7, by retardware

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These DIP DACs were socketed because they failed quite often.
So you might try changing it with another one, and see whether this makes a difference.

Reply 5 of 7, by zyga64

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retardware wrote on 2021-10-26, 09:47:

These DIP DACs were socketed because they failed quite often.
So you might try changing it with another one, and see whether this makes a difference.

This might be a good point ! https://youtu.be/MZvCcadwblg

1) VLSI SCAMP /286@20 /4M /CL-GD5422 /CMI8330
2) i420EX /486DX33 /16M /TGUI9440 /GUS+ALS100+MT32PI
3) i430FX /K6-2@400 /64M /Rage Pro PCI /ES1370+YMF718
4) i440BX /P!!!750 /256M /MX440 /SBLive!
5) iB75 /3470s /4G /HD7750 /HDA

Reply 6 of 7, by Albercik

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You guys are awesome !

I'll try DACs' replacing and (if this won't change anything) I'll try replacing the capacitors.

Unfortunately - I have no oscilloscope and I wouldn't even know how to use it (I'm good in soldering, building some arduino-based devices, but that's all I know). However... I have a AT power supply tester (yes - it's dummy device) and it shows no problems. Using a multimeter gave me 4,8V for 5V rail and 12,1 for 12V rail (I assume that 12V rail has slightly higher voltage due to lack of harddrive in the PC - I use CF card).

I'll get back as soon as I'll perform the tests.

P MMX 166MHz, 64 MB, S3 Trio64V2/DX, SB Vibra 16 ISA, 40GB HDD
P III 650MHz, 640 MB, nVidia Riva TNT2, SB 16 ISA, 120GB HDD
486 DX2 66MHz, 16 MB, Trident TVGA8900C, SB Vibra 16 ISA, 2GB CF

Reply 7 of 7, by root42

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Oscilloscopes are not that hard to use and can be had for ~200 EUR for ones that work with our old hardware reasonably well. That is still no small change, but I have been very happy since I got mine. It helps a lot in diagnosing problems. Simply seeing that signals have too low a level or odd shapes makes troubleshooting much, much easier.

Also, swapping the RAMDACs is a good idea indeed. They can be flaky and/or weird at times.

YouTube and Bonus
80486DX@33 MHz, 16 MiB RAM, Tseng ET4000 1 MiB, SnarkBarker & GUSar Lite, PC MIDI Card+X2+SC55+MT32, OSSC