Moon Patrol Sound

ItsJustaGame

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My Moon Patrol game was working great. The sound crackled, faded a bit, and now doesn't work. Probably the caps or the amp or something, but I can't fix it because I just don't have the skills. Can anybody help repair it or at least guide me down the path of an attempt? Where can I find the right caps and the right amp? Is there anything I can check that is common for these sound pcbs that won't require me to #$@$ it up with my arthritic soldering fingers?

I know it's not the power because I had the original power pcb running and transferred it over using a switcher. No luck. Exact same beautifully playing, but sound-less game. :(
 
Crackled, faded, then died completely. My first guesses would be loose/disconnected wire or header pins. Check from the speaker terminals back to the PCB. Same for the volume pot if it's located off the PCB.

If those check out ok, double check power with a meter. Switcher be damned, that's no guarantee that there's correct power coming into the sound board. Check the fuses while the meter is out.

If that all checks out, my next guess would be the amp. Or amps.
 
Check that you have 12V coming from the power supply - without it the game will run perfectly but no sound as the audio output amplifier chip is the only thing on the board that uses the 12V.
 
Yep, 99% of lost sound on a MP is because your 12volts is low.. Have owned a few and ran into this issue.. Rebuild the original ps, or buy an adaptor for a modern ATX ps.. I have these available, arcadeshop also sells another type.
 
Thanks, guys. I replaced the amp and a couple of caps on the sound board today and it is actually working right now! I have never been able to fix anything like that before! The voltages I checked and double checked. All seems well. Thank you again for helping.
 
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