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Taito Frontline arcade pcb repair

Game did not boot and just displayed a solid color screen. The Z80 cpu, located on the lowest board of the 4 board set didn’t show any activity with a logic probe. It hadn’t failed though – instead the WAIT line was being held which prevented the CPU from doing anything. There are actually 4 different potential sources for WAIT on these boards, so any of them could have failed as well as the OR gate that combines them. Testing with a logic probe revealed a bad LS74 which was replaced and the game could now boot.

frontline

Quite obvious though that some graphics were wrong. Frontline and other Taito SJ games are a little bit unusual – instead of the graphics hardware directly accessing the graphics ROMs, the graphics hardware draws out of RAM. So the CPU has a banked port into the graphics ROMs which it copies to video RAM as needed.

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So in this case the problem wasn’t actually on the video board, but in how the CPU was reading the ROMs. The schematics show a bunch of 40193 chips that control the address lines for the graphics ROMs. One of these had failed – a logic probe showed dead outputs. A replacement was fitted and the game was 100%.

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