Taito Twin Cobra arcade pcb repair
A slightly unusual fault as this board stalled on the check screen, but reported everything ok. If RAM, ROM and sound are ok then why doesn’t it work? Without much to go on I fired up MAME to see what the CPU is actually doing at that point in the debugger. The answer is the 68000 starts communication with the TMS32010 protection microcontroller. Disabling the microcontroller in MAME made the emulation act like the physical board as the main CPU waits forever on the protection response.
On the real board the TMS32010 is hidden under the T.TC-4 sticker. A logic probe showed it was getting a clock signal but most data and address pins were weak or dead. The game booted perfectly using the T.TC-4 from another parts board, so that confirmed the microcontroller itself was dead. Replacement is the only option as I don’t think blank versions of this part are available anymore.