![]() ![]() Z80s are a very common failure on these, some rumours say they used slower Z80s and drove them faster than they were designed for, but on the ones I fixed the Z80s were marked correctly. If you hear nothing then press hard with your finger on the pins of the amp chip on the underside of the PCB (take any metal rings or watches off first), this should get you an angry buzzing noise, if you can change the volume of that with the pot then the amp is fine. You can test the Amp chip by turning the volume pot up and down, if you hear a crackle or hiss that you can change the volume of then the amp and associated caps are healthy. The odd one out was really odd in the fact it had never had a heatsink on the amplifier chip and over the years all the pins on the amp chip had cracked through lack of physical support. I have fixed literally dozens of CPS1 boards that had no sound and all except one had a bad Z80 as the sole cause. If the board has no signs of damage then I would go straight to replacing the Z80 CPU on the lower board.
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