Mortal Kombat 2 Audio issues

dab0ne

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My Mortal Kombat 2 cabinet is working great except after about ten minutes the audio goes out completely. If I leave the cabinet off for a bit it seems to fix itself, but then after about ten minutes the audio goes out again. Sometimes when I turn on the cabinet the audio will sound muted for a bit before going out. I've also heard strange, high pitched noises, coming from the speakers kinda like feedback or something. I'm assuming either I need new speakers or there's something wrong with the power supply but not totally sure. Any insight to this issue would be greatly appreciated.
 
Very unlikely it's the speaker. Possibly could be the power supply but most likely the issue is the sound board. These midway sound boards have been dropping like flys lately. Working MK2 sound boards are currently selling for more than main boards if you can even find one.
 
OK. Thanks for the replies. Phill Bennett was kind enough to take a look at the board and fix it recently. It didn't work at all until then. I'll send him a message, which is what I probably should have done before starting this thread, and see what he thinks.
 
Keep in mind two things:

1: Mortal Kombat 2 will play the audio for the first few go throughs of the attract mode, then it will turn off the audio to save the ears of owners and arcade operators. If you start playing a game the audio comes back. In your post, you didn't mention when the audio going out is taking place. If it's happening in attract mode IT IS PERFECTLY NORMAL! :D

2: There will always be a hum inside of an MK2 cabinet. The design of the cabinet and the PCBs results in a ground loop being picked up by the speakers. To eliminate this, you'll need to use a ground-loop isolater. There are some threads here on the forums that will outline what needs to be done. Basically, you just put an audio isolation transformer in the speaker line to separate the speaker signal from the ground altogether and eliminate the hum.

So overall, it sounds like your MK2 cabinet is working perfectly fine. :)
 
Ok didn't know about the isolator, thanks. The audio cutting out happens during mid gameplay as well. It stays off unless I power down the cabinet for an extended period of time. If I turn off the cabinet then immediately turn it back on the audio is still gone.
 
That's definatly an issue then. Try reseating your ribbon cable. It could be cold solder joints or leaky capacitors but it sounds like your sound board was just gone over so those things are unlikely to be the issue.
 
OK. I'll try resetting the cables and see how that goes. Thanks again for the help guys/gals.
 
did you consider maybe trying to play the game when the sound goes out?

also as noted, Midway weren't exactly like Capcom with their attract sounds, they do go out after a certain period of time until coins were dropped again or in the case of MK2, pulling down on the joystick to show the high score table may have made it come back? (I'll test this eventually :) )

the buzzing hum is just a feature. leave it alone.
 
did you consider maybe trying to play the game when the sound goes out?

also as noted, Midway weren't exactly like Capcom with their attract sounds, they do go out after a certain period of time until coins were dropped again or in the case of MK2, pulling down on the joystick to show the high score table may have made it come back? (I'll test this eventually :) )

the buzzing hum is just a feature. leave it alone.
He did mention the issue is happening during game play rather than the attract mode. Also not a hum but random beeps and high pichted noises. Fairly certain he's got genuine sound board issues.
 
It's definitely the board. I have another sound board that I was able to test today when I got the time to pull the cabinet away from the wall, open it up, and switch them out. The second board doesn't work properly either but it works well enough to give me some audio feed back and confirm that the problem with is with the original board itself. I should have tested the other board first before making this thread, I guess I just didn't consider it to be the board since it would work then shut off, then work again over time. Thanks again for helping me troubleshoot this issue guys, I really appreciate it.
 
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haven't had an MK2 sound board break yet, knock on wood.

I have a whole stack of RevX ones though. :) which I think it just limited to some communication failure with the main boards.

what I do know is the caps Williams used on the ADPCM and DCS1 boards are not good. they leak.

the DCS boards require -5V, absence of that or it being vastly out of tolerance will make all these "interference" issues magnify by about 1000x.
 
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