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Trident ISA card picture issues

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First post, by wbahnassi

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Hi. I have this Trident ISA VGA card TVGA 8900C that's giving me an annoying picture. Basically the colors are overbright and a little over-saturated, but also there is this annoying vertical stripes pattern too. It's hard to capture on camera, but here's a photo that hopefully demonstrates the issue:

The attachment 20220813_094407.jpg is no longer available

This issue happens despite testing different monitors. But some seem to be less susceptible than others, but never 100% good. On my LCD it looks really bad. Other cards I have dont have this issue. Also tried the card in different mobos, and it's the same.

Here is a photo of the card's boot screen, which shows the BIOS information:

The attachment Screenshot_20220813-094639_Video Player.png is no longer available

Here is the card itself:

The attachment 764_fcc_id_hng2ypvga96x8c21_trident_tvga8900c_top_hq.jpg is no longer available

The stripes become less obvious in darker colors. But damn.. EDIT's blue screen is so blue your eyes would implode. Any idea what can I do here?

Cheers!

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Reply 1 of 4, by pixel_workbench

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I saw the same problem with numerous ISA and old PCI graphics cards. My guess is the cards have a low quality analog output that shows the vertical banding on LCD monitors, but may have been unnoticeable on old CRT monitors of that time period. The only ISA card I have that looks good on a LCD is the Tseng ET4000.

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Reply 2 of 4, by pan069

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pixel_workbench wrote on 2022-08-14, 21:36:

I saw the same problem with numerous ISA and old PCI graphics cards. My guess is the cards have a low quality analog output that shows the vertical banding on LCD monitors, but may have been unnoticeable on old CRT monitors of that time period. The only ISA card I have that looks good on a LCD is the Tseng ET4000.

Just because a card has a ET4000 chip on it doesn't mean you won't experience the vertical banding. I have a number of these cards with ET4000 chips on them from different manufactures and some have this issue and others do not. My Trident with a TVGA9000C on it and it doesn't have this issue.

Edit: I still have to test this with my OSSC to see if that makes a difference...

Reply 3 of 4, by wbahnassi

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Got another Trident 8900C that has a slightly different board layout, and it has no issues. Now I wonder if the over-brightness/over-saturation I have in the other 8900C was from the factory, or if certain components started to cause it with time.

Turbo XT 12MHz, 8-bit VGA, Dual 360K drives
Intel 386 DX-33, Speedstar 24X, SB 1.5, 1x CD
Intel 486 DX2-66, CL5428 VLB, SBPro 2, 2x CD
Intel Pentium 90, Matrox Millenium 2, SB16, 4x CD
HP Z400, Xeon 3.46GHz, YMF-744, Voodoo3, RTX2080Ti

Reply 4 of 4, by rasz_pl

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you could try soldering couple capacitors to DAC supply pins (100uf,1uf and 100nf in parallel) for laughs

https://github.com/raszpl/FIC-486-GAC-2-Cache-Module for AT&T Globalyst
https://github.com/raszpl/386RC-16 memory board
https://github.com/raszpl/440BX Reference Design adapted to Kicad
https://github.com/raszpl/Zenith_ZBIOS MFM-300 Monitor

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