Another Voodoo3 repair attempt - asking for suggestions/ideas \ VOGONS

Another Voodoo3 repair attempt - asking for suggestions/ideas

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First post, by konc

Posted on 2024-05-08, 10:49

konc Offline

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Hi guys, another Voodoo3 repair attempt thread. I got this card in a sad state as non-working. It was missing the bracket, the heatsink, the 3 capacitors on the right and the one next to the feature connector.

But it's working, Glide included, and no stability issues so I thought it's worth the effort.
The issue I'm having is bad output with "trembling" characters. It's related to the resolution/refresh, for example the BIOS/POST screen looks only a bit blurry, while in the DOS mode the problem is worse and apparent.

This video demonstrates the problem, it might be too compressed by the hosting site but it still accurately shows what the characters look like. If anyone wants to see another recording or photo please let me know.
https://imgur.com/dwKSB0o

I did solder the 4 missing capacitors and while I was at it I changed the other 4 electrolytic as well. Also the computer/monitor/power/cables etc are irrelevant. The card has the same behavior in a completely different environment and, the opposite, another identical card works fine in the test system.

So, any ideas what might be causing this? Any suggestions for actions?

Reply 1 of 7, by konc

Posted on 2024-05-16, 10:57

konc Offline

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bump

Reply 2 of 7, by Tiido

Posted on 2024-05-16, 12:01

Tiido Online

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This looks like pixel clock generation issue, likely in the analog domain. You'll probably have to carefully inspect some passives around the main chip, maybe even replace a tantalum.

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Reply 3 of 7, by nuno14272

Posted on 2024-05-16, 12:49

nuno14272 Offline

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I woult try a bios re-flash.

1| 386DX40
2| P200mmx, Voodoo 1
3| PIII-450, Voodoo 3 3000

Reply 4 of 7, by konc

Posted on Today, 10:02

konc Offline

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nuno14272 wrote on 2024-05-16, 12:49:

I woult try a bios re-flash.

I took the opportunity to upgrade to the latest version, but as expected it didn't make any difference.

Tiido wrote on 2024-05-16, 12:01:

This looks like pixel clock generation issue, likely in the analog domain. You'll probably have to carefully inspect some passives around the main chip, maybe even replace a tantalum.

Bummer, I did desolder and check the 5 yellow tantalum capacitors around the main chip and they all measure fine (10-11.5 μF). Also I soldered them back in different positions, just to be extra safe, but nothing changed. Then I checked for shorts (continuity/near zero resistance between the poles) all the small capacitors and resistors in circuit, but none beeped. My inexperienced eyes see nothing suspicious around the chip, if anyone spots something please say so!