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[MPU Mecca]

I am trying to repair the audio on my Barcrest Stop The Clock.

Originally the machine had a MPU4 Mod 2 board which I have but apparently that had an audio fault so a new MPU4 was fitted. However the replacement was a Mod 4 with no audio chip so it was assumed that the fault was elsewhere (previous owner thought cartridge was at fault)


I have fitted an AY-3-8912 in the DIL socket of IC10 of the MPU4 Mod 4 board and I now have some sound. It doesn't sound right and some sounds are missing.

The speaker is OK, tested another speaker and same result.

Is there a circuit diagram for MPU4 Mod 4? I can see that there's one for the Mod 2 so looking at that I suspect electrolytics C56 and C58, otherwise it could be IC35? Anyone know the reference for that, circuit diagram is not clear.



Also I just discovered that one of the fuse holders and fuse is missing from the PSU, however the machine seems to play fine apart from payout. When it pays out you can hear the click click click per coin release but no money is released. None of the tube monitor level units are connected, they're just lying in the cabinet, however the levers that I assume should be sticking out are not so it looks as though it should behave as if coins are present.

Is one of the PSU outputs just for coin release? Any reason to disconnect just this fuse?

Cheers

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