I found this very interesting thread - I've got a `diamond Monster 3D PCI 4MB, Voodoo 1 which was not being recognized.
As mentioned, re-flowing the (very oxidized) pins of both FBI and TMU made it detectable. However, the TMU is still nowhere to be seen, it shows as "dead" as in the screenshot above.

I've re-reflowed the TMU, checked the connections between FBI and TMU with my multimeter, checked all resistor/resistor pack/inductor on the board (though I checked on the component itself) and I cannot find anything out of the ordinary. Of course I checked and re-checked the FBI/TMU legs under the microscope.

I've inspected for damage and I see none.

If I understand correctly the TMU is only connected to the FBI and the RAM so if the FBI is being detected, then I don't need to worry about the PCI connection? Though I checked every single gold finger as I could see a little corrosion and I thought maybe one of them was disconnected.

Any ideas?