This is my original Voodoo 1, a Diamond Monster 3D rev D. A while back it was starting to randomly lock up after varying periods of gaming, eventually
deteriorating to the point leading to the screen below upon trying to start anything.
I was thinking the worst as in bad FBI or TMU but thanks to a fantastic repair video by vswitchzero https://www.youtube.com/watch?v=tRFucW4uB5k I got some ideas.
I have been able to do some diagnostic tests leading to the hopefully accurate conclusion that it has 1 or more bad ram ics connected to the FBI chip.
Testing only in Dos with TombRaider I started by playing around with the SST settings for the TMU in autoexec.bat.
I tried turning it off or on and running with 0, 1, 2 mb ram.
That was giving some non repeatable symptoms. Sometimes the game would run without any texture mapping, sometimes not. Other times
the game didn't run at all just exited with a cannot load texture map error.
The last thing I tried was to alter the amount of ram available to the FBI chip to 1MB and that got Tomb Raider up and running albeit with random
glitches. I had already tested all pins on the FBI and TMU ics, they are solid. I did resolder the ram chips and then tested all the pins connections to
the FBI chip and again there are no issues there.
So next step is to remove and replace the ram ic's connected to the FBI chip. All textures are good so will say highly unlikely any problems with the TMU or the 2MB ram.

I hope this helps some people as there are very few voodoo 1 repair videos or blogs anywhere and a lot more for voodoo 2's.