My Taxi has lost its sound. It worked fine and now no sound, just a constant hum. From the moment the power is flipped on the hum starts. The usual “BONG” noise does not happen. The game boots up fine and a game can be played without any other issues, everything works as it should. The cabinet volume control does not change the volume or loudness of the hum. The sound test button on the MPU does not do anything either. I read in a different post that the hum can be caused by a grounding issue so I made sure that all of the screws for the audio and mpu boards were tight. No change. I disconnected and reconnected all of the jacks that run to the audio board and the large jack that supplies the power from the power board. No change. I’m up for suggestions. I’m suspicious of the Yamaha YM2151 chip. See the pic for a good look at the Yamaha chip.

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Voltages checked out ok. Working from right to left I got +4.93, Ground, -14, and +12.

I also swapped out the sound board from Rollergames into Taxi and vice versa. Taxi will boot up with the normal BONG tone as it should. Rollergames now has no sound but does have the hum, so it’s definitely something wrong on the sound board. How do you troubleshoot a soundboard???

I thought I would check the capacitor readings while I had both boards out and found the following readings. It seems like C32, C29, and C12 are all reading much lower than Rollergames. Also, C26 on Taxi had continuity while C26 did not on Rollergames. Could these cap differences be the issue?

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Bump for advice

Capacitor C26 was the issue. It had continuity when I checked it while on the board. After removing and replacing the cap all is well. No hum and the sound board is functioning properly. The moral of the story is never trust a cap with continuity, it’s bad...