Troubleshooting help plan for the 3dfx Voodoo 2 series cards
Before you start a first repair attempt, take a close look at the pins of the three 3dfx chips. Many have several bent legs that were shorting out. If you find this, first straighten out all bent legs. Many in the free second-hand trade come from people who have pulled them from the scrap somewhere and sell them as untested under the pretext of so many imaginative excuses.
Furthermore, it is very helpful, before starting to replace components, to first check all pins of the three 3dfx chips for their soldered connections to the PCB. Due to the age, contact resistances can be present here. Further troubleshooting is only useful when all chips are well soldered.