I have a few VGA ISA cards lying around that are broken. Two don't even produce an error beep when I plug them in, everything just stays black. The third produces a yellow blinking cursor, but nothing else.

The cards are two Trident (8900 and 9000) and one S3 based card.

The question now is, how do I proceed with trying to revive them? Shall I measure at certain pins if VCC or GND is correct? Could it be that the BIOS has degraded after 20-30 years those cards have been in existance? If so, how can I test this?

Any other ideas?