Don't you need to disable the onboard VGA before putting in a VGA card? I'm surprised either 8900 worked.

There's a related discussion going on over here, potentially Re: Suntac 80286 Mainboards

jakethompson1 wrote on 2025-07-01, 22:27:

Don't you need to disable the onboard VGA before putting in a VGA card? I'm surprised either 8900 worked.

Yes i did, test with both enable and disable.

It could be a problem with 16-bit ISA connection. Some VGA cards work fine with 8-bit ISA.

amontre wrote on 2025-07-01, 22:23:

I have this Acer 386sx/33 (with acer 100-t) motherboard that is very picky on the ISA vga card. So far it only work with Triden […]
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I have this Acer 386sx/33 (with acer 100-t) motherboard that is very picky on the ISA vga card. So far it only work with Triden 8900c and 8900CL-B. It refuse to work with the likes of 8900D, CL GD5420 and GD5422 (which all i have tested working on my 486DX2) . When i tried those cards it has 3 beeps as video below.

https://youtube.com/shorts/45ivPYP2LQk?si=WzfzpT2qxqj2305s

Motherboard close up;

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Incompatible VGAs;

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Could it be a missing OSC signal on the ISA slot? All the cards you pictured have no crystals and I know that that design of CL-GD5422 ISA card doesn't work on some of my boards because the OSC signal is missing