Need some serious help with MK2 sound

[Love5508]

I just got a Mortal Kombat 2 jamma board complete with the sound board and all the wiring.  Its revision 3.1 and looks like new.  I installed it into my MK4 cabinet and everything looks great EXCEPT....there is this constant annoying hum in the back ground.  Doesnt matter how loud or quite I make the volume, the static sounding hum is always the same loudness.  This does not happen with my MK4 board.  I checked all the power and I am getting the correct -5v to the sound board.  Its a hum that normally I would say is interference of some sort BUT when the game starts playing a demostration, the hum changes pitch depending on what is happening on screen...if the screen changes quickly from one frame then blacks out and goes to another, the hum goes with it.  I have heard a new power supply may fix this issue but I think I may be in denial.   

[Love5508]

I just read on these forums that the MK2 board uses p12, player 4 harness...hmm I have player 3 harness installed but I dont think that would cause this type of issue.  All my controls work fine.  Im stumped...

[Malenko]

do you hear the hum when you put the MK2 in another cabinet? have you reseated the sound ROMs?

[jcterzin]

if it changes with the video, could be your monitor. Are you saying that you used the same monitor when you tested the MK4 board?

[Love5508]

Every thing tests fine when i swap my mk4 pcb into the cab.  No monitor or sound issues with mk4.  I only have this one cab.  This sucks.

[Malenko]

Where do you live? maybe someone local can let you test their MKII in your machine or let you test their MKII in your machine?

does the game pass all the RAM/ROM checks?

[Love5508]

I live in langhorne, PA about 20 minutes north of philly.  All roms pass and when i check in the sound board test, that passes too.  I dont think its the board since everything works other then the hum but i dunno.

[BobA]

Check this older thread might help.
Link to thread re MK2 sound

[Love5508]

Yeah i read that thread already but thanks for the help!  I think i found out the issue here. I was testing with the multimeter i have and realized that when i turn the voltage knob on the power supply that the voltage does NOT increase or lower.  It is always set at -4.99 volts for the audio wire.  I think if i get a new power supply and turn it up a bit it "should" fix it.  Keep you all posted!

[Malenko]

I'm in Newark,Delaware not too far away if you wanna make the drive I have a dedicated MKII cab.......
but it does sound like a voltage issue.

[Love5508]

Brand new direct replacement power supply came today.  I hooked it all up and made my voltages all set good BUT...NO WORKY!   It still produces the weird buzzing but I notice as I adjust the voltage, the buzzing changes in frequency with the adjustments.  For example if I turn it down, the buzzing will get low pitched and "slower" and if I turn the voltage up, the damn buzzing get higher pitched and "faster".  I can hear the lope of the frequency shifting in tandem with the amount of voltage.  VERY ODD and has now confused the hell out of me.  All other games (UMK3 and MK4) are not affected in any way.  I am about to break the damn board...any one, please, any one?

[MK3FAN]

Brand new direct replacement power supply came today.  I hooked it all up and made my voltages all set good BUT...NO WORKY!   It still produces the weird buzzing but I notice as I adjust the voltage, the buzzing changes in frequency with the adjustments.  For example if I turn it down, the buzzing will get low pitched and "slower" and if I turn the voltage up, the damn buzzing get higher pitched and "faster".  I can hear the lope of the frequency shifting in tandem with the amount of voltage.  VERY ODD and has now confused the hell out of me.  All other games (UMK3 and MK4) are not affected in any way.  I am about to break the damn board...any one, please, any one?

Make sure your ribbon cable is hooked up correctly. Sometimes weird things happen it it gets turned around at one end or the other.

[Love5508]

Ribbon cables are set in correctly.  I dont know, may just be a bad board.

[MKFan4Life]

I have a dedicated MK2 cab and it has always exhibited this phenomenon.  I have swapped other JAMMA boards into the cabinet and they don't do this.  WEIRD.  When playing the game at a reasonable or loud volume you don't really pay it much attention, but at lower volumes I hear it...like a hum or whine.  When my screen changes during attract mode, it makes a little squelching sound as the screen changes from like the winning streak display to the next screen.

I thought maybe that one large capacitor on the sound board might be bad (possibly filtering the power supply?), and changed it out with a new one of the same value, but there was no difference.  I also have another MK2 JAMMA board set I have tested to make sure it works properly, but I didn't think to see if it exhibits this "interference".  I don't think either my MK1 T-Unit set or MK1 knock-off JAMMA boards had this problem.

I will try, if I can, tomorrow, to hook the other board set for MK2 up in the MK2 dedicated cab and see if I notice it doing the same thing.  Would be nice to find out the cause once and for all, lol!