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System 12 Tekken 3 No Video, Plays Fine

tomoro__

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I have a Tekken 3 board that needed a lot of work, no boot when I got it, recap plus a couple broken trace jumpers later it boots but shows no video whatsoever through JAMMA. I feed it through a GBS, and initially got a no signal feed, but now get a dark gray screen. It plays enough that I could win a set blind. I currently don't have a JVS setup, need to order a couple cables, so I haven't tried there yet.

For whatever reason, it also won't go to the test menu, as when I flip that dip switch, the game still starts.

So far, I've reflowed the GPU and RAM chips on the CPU board, and tried resoldering the dip switch, with no changes. There was also a bridge on the bottomside of the GPU that I removed, but it didn't change anything either. Green wires and the small jumper on the underside of the main board were there when I got it, and at least the jumper seems to be stock for early revs.

Hopefully someone else might have any idea what's up, because I'm stumped at this point.
 

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Update, Found a solution and now have (garbled) video!
Following the excellent work of City Game on youtube (
View: https://youtu.be/OsxSpCeLcEA?si=zyUbO60DWKw4IaEa
) thanks to autotl, I tested pins 1 and 13 on the CXA1779 on the mainboard to check voltage. It requires 12v to run, but, same as City Game, got 4.something, showing that the voltage boost chip 10D nearby was bad. After ensuring connections were good between the chips (no oscilloscope yet), I swapped out 10D, a TI TPS6734I (https://www.digikey.com/en/products/detail/texas-instruments/TPS6734IDR/370117) and the CXA1779 is reading fine, and video is visible!
Just gotta sort out the graphical issues now...
 

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