Mortal Kombat 2 sound board problem.

Thanks for the input. Yes, I have tried another board, my UMK3 works and sounds fine in that cab.

Broodwich said:
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?
Click to expand...
 
The MK2 sound board I have looks almost new. No scratches, burns, rust, or even dust on it. I took out all the proms on it and there is no rust or corrosion on any of the pins or anywhere on the board. All the pins were in the sockets. I have also looked at the bottom very close a few diffrent times and have found no problems nothing touching or burned or anything. I have not checked the voltage yet as I dont have access to a volt meter right now but i also tried it on another mk2 board I have and still nothing.
 
if you wanna settle the +5 business once and for all, I encourage you meter each rom on the sound board for +5.

assuming the U-shaped notch is to the left, you want to meter the pin in the lower right corner (ground), and the pin in the upper left corner (+5).

here's a visual aid for you: http://wiki.xtronics.com/index.php/File:Pinout2716.png

if there's no +5 present, then there's a likelihood that your harness is damaged. the next plan of attack would be to meter it at the main board's molex connector, ensure that +5 is coming out of it, then you test it at the sound board's molex connector.

then meter for continuity from the main board's +5 connection to the sound board's. if there's no continuity, you have a break in the wire. which could very well explain why you have +12 to operate the amplifier (to generate the hum) and no tones, because the software isn't being powered.

what still doesn't make sense is that you're getting IRQ DETECTED messages... as I mentioned before, I had a software issue with my game roms (the mains) and that was throwing the sound board for a loop, playing the wrong sounds and everything (despite the sounds being in the roms on the sound board).

also, for the hell of it, check the -5 too.

here's the game manual for pinout information: http://arcarc.xmission.com/PDF_Arca...s/Mortal_Kombat_2_(16-40029-101_Oct_1993).pdf
 
Thanks for all the info. I will try all this and see. It will be Saturday before I can work on this again but I will let you know what happens, thanks.

mecha187 said:
if you wanna settle the +5 business once and for all, I encourage you meter each rom on the sound board for +5.

assuming the U-shaped notch is to the left, you want to meter the pin in the lower right corner (ground), and the pin in the upper left corner (+5).

here's a visual aid for you: http://wiki.xtronics.com/index.php/File:Pinout2716.png

if there's no +5 present, then there's a likelihood that your harness is damaged. the next plan of attack would be to meter it at the main board's molex connector, ensure that +5 is coming out of it, then you test it at the sound board's molex connector.

then meter for continuity from the main board's +5 connection to the sound board's. if there's no continuity, you have a break in the wire. which could very well explain why you have +12 to operate the amplifier (to generate the hum) and no tones, because the software isn't being powered.

what still doesn't make sense is that you're getting IRQ DETECTED messages... as I mentioned before, I had a software issue with my game roms (the mains) and that was throwing the sound board for a loop, playing the wrong sounds and everything (despite the sounds being in the roms on the sound board).

also, for the hell of it, check the -5 too.

here's the game manual for pinout information: http://arcarc.xmission.com/PDF_Arca...s/Mortal_Kombat_2_(16-40029-101_Oct_1993).pdf
Click to expand...
 
I don't know if this will help determine anything, but I forgot to mention something I did when tinkering with this board. I had it hooked up and it was not playing sound. There is an AUX IN and AUX OUT on the board. I hooked an external sound source to the AUX IN connections and I did get sound through the speakers. I think this is a definite yes that the amp is working. Just thought that may give some more insight on the problem.
 
Last edited:
Here is where Im at I checked the 12v at the molex connection on both ends of the cable and Im gettin 12.5v on both ends. At the +5 im getting 5.1v at both ends and at the -5 Im getting .6v on both ends. As for the roms I get 5.1v on all the roms I tried the 12v pin and didnt get anything 0v and the -5 on the roms I also get 0v. I also checked the speaker wires in the molex and get 6v outta both.
 
you have like non-existent -5 there. just saying. peculiar that the other games work. must be your wiring.
 
What would be your suggestion to do? I should change the -5v wire in the molex harness? Im pretty new to getting into the electrical end of this so im sorry if I sound dumb or ask dumb questions. I appriciate the help alot. If I could get this to work I would be so excited cuz Ive been looking to buy another soundboard and really dont want to if I could get it to work.
 
Have you checked the -5 coming straight out of the power supply? It is possible for the ps to be bad on just the -5 part I think. If it checks out good there find the -5 pin on the jamma connector and check it there. If it's good at the ps and not at the connector it's a wiring problem.
 
Ok i feel stupid after looking at the jamma harness I see the -5v wire is not even hooked up to the power supply. Let me give you alittle background on what im working with. Its a homemade supergun i bought that was used with street fighter alpha. I took that out and have been playing the midway games. My nba jam sound works cuz it dont need the -5v for sound. He had only the power button lights wired to the -5v. So next dumb question if i connect the 2 -5v wires from the jamma harness up to the ps i should put a fuse between right? What kind of fuse would be good to put inline? Also I noticed the video ground wire is also not connected. It has a jrok encoder but getting an ebay hd converter and slg3000 soon. Should the video ground be connected and where to? Thanks again I have been looking info up but dont wanna try anything and fry games or cuz any other probs.
 
Ok I hooked the -5v up to the power supply and the games starts and I now hear 1 tone. I went in to the test menu and went to sb test and I get 1 tone saying sound board checks good. Go into the game and still nothing. Played sounds under test menu and nothing. I checked the -5v at both ends of the molex and get -5.1v at both ends. I checked the roms at the -5v pin and still reads 0v.
 
I have +5 present at all the rom chips. I also have +5 present at the led. I have discovered when I short pin 4 on chip U29 the led comes on. I don't think U29 is bad because the voltage on the other pins seems to be correct, although it may be. Are we absolutely sure that the led is supposed to be on ALL the time? I don't know what this means exactly but if this means anything to anyone, let me know what to try next.

Thanks


mecha187 said:
if you wanna settle the +5 business once and for all, I encourage you meter each rom on the sound board for +5.

assuming the U-shaped notch is to the left, you want to meter the pin in the lower right corner (ground), and the pin in the upper left corner (+5).

here's a visual aid for you: http://wiki.xtronics.com/index.php/File:Pinout2716.png

if there's no +5 present, then there's a likelihood that your harness is damaged. the next plan of attack would be to meter it at the main board's molex connector, ensure that +5 is coming out of it, then you test it at the sound board's molex connector.

then meter for continuity from the main board's +5 connection to the sound board's. if there's no continuity, you have a break in the wire. which could very well explain why you have +12 to operate the amplifier (to generate the hum) and no tones, because the software isn't being powered.

what still doesn't make sense is that you're getting IRQ DETECTED messages... as I mentioned before, I had a software issue with my game roms (the mains) and that was throwing the sound board for a loop, playing the wrong sounds and everything (despite the sounds being in the roms on the sound board).

also, for the hell of it, check the -5 too.

here's the game manual for pinout information: http://arcarc.xmission.com/PDF_Arca...s/Mortal_Kombat_2_(16-40029-101_Oct_1993).pdf
Click to expand...
 
I'll take a look later. I honestly don't recall lol

I would think that it's supposed to come on when it plays sounds.
 
I checked before I posted it the first time, and I just checked again..... the led on the sound board stays on while the maching is turned on. This is on my original dedicated MKII.
 
I have still had no luck finding why my sb will not work. The led on the board comes on when you first turn the power on you hear a dong and stays on during rom check. Then the light goes out as the game starts. You go into test menu and its off until u go to general sound test it has 1 dong like the board is good but then the light goes out after u leave that screen. It will not play or make any other sounds. All the voltage seems right at the harness the rom voltage is good except the is 0v at the -5v on the rom. The game will also randomly dong after the game has started. Any more leads on where to go next would be a great help.
Thanks
 
Ok thanks. I am just having trouble determining what is failing. Like I said my led never comes on. Along with the humming in the speakers I can hear some whirring and buzzing occasionally very faintly. It seems to change as the processor does different things. Hopefully I can pinpoint the point of failure with you guys help.

THE COUNT said:
I checked before I posted it the first time, and I just checked again..... the led on the sound board stays on while the maching is turned on. This is on my original dedicated MKII.
Click to expand...
 
OK. After trying all the tips I've gotten and all the probing I have done, me and my buddy think the U29 chip may be bad. The way I look at the schematics and board, it is tied to the led that doesn't come on and it's part of the reset section. I think the reset is never going high so the sound board CPU isn't booting. I may be totally off here but that's what it looks like to us. I am going to get a logic probe and check the reset section tomorrow and see if it goes from low to high or stays low(which I think it is doing). I might change out that chip anyway. It's only $2.50 so why not. Does any of this sound plausible? Thanks for any input.
 
action76 said:
OK. After trying all the tips I've gotten and all the probing I have done, me and my buddy think the U29 chip may be bad. The way I look at the schematics and board, it is tied to the led that doesn't come on and it's part of the reset section. I think the reset is never going high so the sound board CPU isn't booting. I may be totally off here but that's what it looks like to us. I am going to get a logic probe and check the reset section tomorrow and see if it goes from low to high or stays low(which I think it is doing). I might change out that chip anyway. It's only $2.50 so why not. Does any of this sound plausible? Thanks for any input.
Click to expand...

for $2.50 it's worth a try
 
Well the U29 chip did not do the trick. I still think it has something to do with the reset circuit but I don't know what piece is the fail point.
 
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