Mortal Kombat 2 sound board problem.

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My sound board on Mortal Kombat 2 is not producing any sounds. I am getting a light speaker hum when the volume is turned up but no hum when the board is not hooked up. The red led never comes on or blinks (when is it supposed to?) When I go into the sound diag it get the irq is detected and good but no tones. The data cable is hooked up right. I was curious about the -5 volts which seems to be a problem from what I read. So I checked the PS the 5V is 5.08 the 12V is 12.04 but the -5V was -4.3. Is that too low. The wierd part is when I checked the pins on the Main PCB and the sound PCB I was getting -5.01V (how is that possible. Any help is appreciated.

Thanks,
Stephen
 
the -5 will always be off, as will the +12... it's not entirely uncommon to see that above 13 volts.

considering you have speaker hum means that the amplifier is working on the sound board, so the sound board IS working.

have you checked the Volume Adjustment section of the test menu by chance? I'm not entirely sure if you'll hear tones or not if that's turned all the way down. :)

you can additionally go into Utilities and do the Full Factory Restore, see if that helps. perhaps it's NVRAM (battery backup) corruption causing the volume to stay low. although, I've never heard of that happening with Midway's stuff... usually happens with the Capcom CPS2.

also, if the -5 was absent..... you will know. trust me.
 
The volume in the menu is about halfway up. I haven't tried the factory restore, unfortunately it will be next weekend before I will be able to try that, but I definitely will.

Thanks
 
if that still doesn't get it, then you're probably looking at a cap issue. like I said, I would think the amp is working if you're hearing any hum from the speakers, so it shouldn't be that.
 
Okay, thanks. Do you think it would be a cap on the mainboard or the soundboard?
 
i'm going to ask the obvious question of do you have the volume pot hooked up (is this a dedicated machine or just boardset)? and have you tried lightly pushing down on the soundboard prom chips?
 
I didn't think MK2 needed a volume pot like MK1 does. Although the cabinet it is in (a dynamo hs-5 I think) has a volume pot on a bracket with a credit and a menu button behind the coin door. I have not tried pushing down on the chips (not while it was hooked up anyway.
 
i have almost the same setup for my NBA JAM which is also a T-unit and it needed the Volume pot to complete the circuit and play sound. (volume/test/service switch on door still had to add 2nd dedicated T-unit volume pot).

I could be completely wrong, mecha knows his stuff reguardless :D i'm just a novice at this myself.

and yea i'm not a fan of pushing on chips while the machine is on either but sometimes it works (try this absolutely last).
 
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Well, can someone confirm if the MK2 sound board needs a sound pot attached to the board or not. If it does where does it attach to? I knew MK1 and NBA JAM do but I thought MK2 did not. I am not sure what version of the PCB I have but it is the version that does not have the memory expansion board.

Thanks
 
i think i'm wrong and you might be right not having one i'm looking at some pictures of the board sets and i don't see the volume pot connector anywhere on the soundboard.
 
MKII does not have a bol. pot. The volume is only adjusted through the menu setup.

The red led on the sound board should come one a couple seconds after turning the machine on and then stay on.
 
I agree with Mecha187 that the amp on board is working because of speaker hum and the heatsink on it gets warm like it should when working. The Count said the sound board LED should come on and stay on shortly after power up. If this is the case what could be causing it not to come on? Is it like Mecha said earlier and possibly a cap issue?
 
I agree with Mecha187 that the amp on board is working because of speaker hum and the heatsink on it gets warm like it should when working. The Count said the sound board LED should come on and stay on shortly after power up. If this is the case what could be causing it not to come on? Is it like Mecha said earlier and possibly a cap issue?

Going by the schematics, the red led is turned on by the 5v supply and grounded by chip U36.

Also, have you tried the sound test in the test menu? If not, do so.
 
I have run the sound test. I don't get any tones but it says the IRQ is detected and good.
 
I would try removing and then reinstalling each chip on the sound board.

Also, I would check for the presence of 5v at the red led. One side or the other should have 5v. If it has 5v, then the issue may be in U36. If it doesn't, then you are loosing your 5v somewhere.
 
I find it peculiar that the board is coming up as working if you think it's missing +5. I say this because I had the main game roms covered in corrosion and that would cause the sound board's IRQ function to go intermittent until I sanded the legs.... then my board worked perfect after that.

if software can cause the IRQ issue, and that's not the case here, I don't know what to think.

I too would start reseating the sound roms. reseat them all, even on the main board/memory board.
 
Definitely check the +5 at the sound board to make sure it's there. If the led is not coming on at all it's possible the led is just bad, but I'd bet you are missing +5 for some reason. Dumb question, but I didn't see it asked earlier....do you have the power cable that goes between the sound and main boards? The ribbon/data cable and that power cable are what you need.
 
I have an MK2 sound board with the exact same problem. You can hear a hum from the speakers and even hear alittle of the joystick movments. The light lights up on the soundboard when the game comes on but does not stay on when playing game. Under the test menu it says irq detected but I hear no tones. Everything is hooked up right tried restoring factory setting but still nothing. I feel your pain and it seems very hard to get MK2 sound boards. I have NBA jam sound boards that work but they look alittle diffrent then the MK2 board.
 
The NBA Jam board is definitely different. It is the same as a MK1 board but not 2. What have you done as far as troubleshooting? Reseated the chips, tested for 5 volts at the led, and so on? Just wondering what you might have tried that didn't help. I am going to keep at it and try everything people have suggested. I will let you know if I have any luck.

I have an MK2 sound board with the exact same problem. You can hear a hum from the speakers and even hear alittle of the joystick movments. The light lights up on the soundboard when the game comes on but does not stay on when playing game. Under the test menu it says irq detected but I hear no tones. Everything is hooked up right tried restoring factory setting but still nothing. I feel your pain and it seems very hard to get MK2 sound boards. I have NBA jam sound boards that work but they look alittle diffrent then the MK2 board.
 
it's so odd that they made different T unit sound boards for the different games, there must have been a reason, there's a definite difference in the power harness i know that. how does the bottom of the soundboard look? has it been repaired before? are there any deep scratches (obvious trace damage)?

I think u mentioned earlier testing the voltage at the sound board molex and it was good on the 5v line correct? silly as it might sound but check all the chips on the sound board and make sure all the legs are socketed.

You might as well look at the bottom of the main PCB also for repairs/scratches as they could cause problems also. use some super fine grit sand paper and sand the legs of really dirty/corroded chips till they shine (don't sand a lot just enough to make a better contact)as mecha said. do this carefully as the pins are easily bent/broken and when you remove them from whichever board you are working on, i'd start with the sound board as you can't make it any worse than it is really. Make sure the chips are facing the right direction before and definitely after you pull each one (powering up backwards is BAAAAAAD). Since the game plays i wouldn't mess with to many of the main board proms i'd try and concentrate on the ones that control the sounds only (make sure you check the socket leg solder joints).

Just some more ideas as i read over this post.


Also, do you have another boardset (any jamma game) that you can throw in there to make sure it's not cab wiring or your speakers?
 
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