Mortal Kombat sound issue

Nin10doh

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So, I fired up MK1 today and you can barely hear the sound coming out of the speakers. Went to radioshack to buy a new 50k volume pot, installed it and it is still doing the same thing. Checked the power supply voltage and it checks out good. Any suggestions?
 
Take a wire and short pins 2 and 4 of P5 (where the sound pot connector hooks to). That will eliminate the sound pot and wiring. If the volume doesn't immediately skyrocket, then you have a definite problem with the sound board. I'd start by checking the caps and then the amp.

See if that helps at all.
 
yup do the jumper trick like zeno said, just don't leave it like that for extended periods or you'll (a) burn out your amp (b) blow your speakers.

if the sound goes full blast there's an issue with your wiring mostlikely as you changed out the pot already. I sell a replacement (pot with harness) as well as bob roberts.
 
Ok, so im back to the same problem again.....this time ive replaced all the caps, soldered in a new audio chip, reseated all the roms, reflowed the bottom of the sound board, installed a new ribbon cable, checked all my voltages and there all where there supposed to be. Any suggestions?
 
captain obvious.. got both ends of the ribbon cable facing the same way? red stripe on pins 1/2 on both boards.

also, try the old cable just for fun. see if your new cable is causing it. what else did you unnecessarily change since it quit working again?
 
ya ribbon cables are the right way, tried the old cable and get no sound at all. i just replaced 2 caps that were bad. worked for about a week then the sound went out for a couple seconds then came back on. tried it the next day and you can barely hear the sound again.
 
when you touched up the solder joints you didn't bridge anything on the amp did you?

which, are you getting any amp hiss? or... do you have the pot installed and wired right? without it you won't get sound I guess. lol. for fun, go into test mode -> diagnostics -> sound board test and see if you have a working IRQ.
 
the roms are software. the amplifier is hardware. if you're getting a Sound IRQ OK message, then that means it should be working.

there are wires on the power harness that piggyback the speaker signal from the sound board back to the JAMMA edge. verify those are working now. I believe they're blue and purple wires.. been awhile since I've seen those. verify you're getting continuity between the sound board and your speakers too, use alligator clips to extend.

out of your assortment of parts you replaced I didn't see the amplifier in there. that's the IC that's mounted to the heatsink on the sound board, I would visually inspect it to see if it's blown. it'll probably have a hole in it or something if it's visually bad. or you could just wing it and replace that too, you did everything else already.

beyond that I have no other further explanation as to why your sound board was "fixed" after changing a couple caps and then you decided to replace everything else and now you have no amplifier hiss.
 
ya i did replace the chip on the heatsink, but ill try those wires to see if thats the problem. i fixed it again because i lost amplification, i can turn the volume pot all the way up and it sounds like is is being ran through a little tiny tweeter. no bass at all. thought it was more bad caps and the amp chip so i replaced them and still didnt fix my problem. I rechecked the power cable that runs from the sound board to the main pcb and everything tested fine.
 
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