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TSENG 4000 VLB - dim picture output

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First post, by Jed118

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Hello all,

I have a TSENG 4000 VLB video card, and while it does work, the image displayed is very dim. A CRT deals with it a bit better than an LCD, but it is truly hard to read - the text isn't blurry, if anything it seems gray. I have not found the card on Stason

https://stason.org/TULARC/pc/graphics-cards/VESA_1.html

(my rev anyhow) and I have moved some jumpers around but no change.

tZSsjDj.jpg

Now, the card looks like it's been around, the contacts are worn, but none seem damaged. I ran a white eraser over them to clean them up, they don't seem corroded. I also reseated the BIOS chip and the socketed chip beside it. I have also tried several VLB computers in which my other cards work fine.

It seems to me that it's a low signal issue. Is it the DAC or one of the caps perhaps? What should I try?

I'd like to get this going so I can do a benchmark of two systems that have integrated CL VGA cards vs my new Mach 32 vs this 😁

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Reply 2 of 4, by debs3759

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I'm no expert, but it sounds like one or more of the caps next to the VGA connector might be leaking current to ground.

See my graphics card database at www.gpuzoo.com
Constantly being worked on. Feel free to message me with any corrections or details of cards you would like me to research and add.

Reply 3 of 4, by ALEKS

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Most probably it is the RAMDAC VREF voltage. Check the datasheet of the RAMDAC (yours appears to be a Winbond part) and see what voltage it expects on the VREF pin. Then check with a multimeter if the required voltage is present at the output of the resistor divider next to the RAMDAC. Normally that voltage is smoothed out by a small value MLCC or tantalum capacitor. If that is shorted then the voltage on that pin is pulled low.
If that voltage is not what the RAMDAC expects, then the image will be either dim (or very dim, almost black) or very bright, depending on the actual fault.

If it's not this, then you can probe the tantalum capacitors for shorts.

Last edited by ALEKS on 2021-04-07, 05:44. Edited 1 time in total.

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