Mortal Kombat 2 soundboard repair

Jon Hughes

Member
Joined
Mar 24, 2008
Messages
223
Reaction score
7
Location
Chester, Cheshire, United Kingdom
Hi everyone who's interested,

A while ago there was a thread running on an MK2 soundboard repair by action76. There seemed to be quite a lot of interest in the thread but sadly it just seemed to fade out.

I had 3 soundboards in need of repair (had) and decided to give them a run at repair. From the original thread I noted that the DAC (AD1851N-U16) could have been a problem source - so that would be my starting point.

Board 1 - dead, logic probe on pin 9 (voltage out) of the DAC was dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with a 16 dip dual in line socket and replaced the AD1851N. Powered up, one bong and then the music - nice one, one down two to go.

Board 2 - dead, logic probe on pin 9 & 10 of the DAC both dead, inputs on pins 5, 6 & 7 showing logic. Pulled the DAC (U16) and replaced with 16 dip dual in line socket and replaced the AD1851N. Powered up, no bong but now the diode light is on. Logic probed the whole circuit, all inputs and outputs good leading to U16. The logic stops past U16 into pin 9 so it's difficult to trouble shoot past there with the probe. Noticed U37 (TL084) was warming up and was getting nothing from inputs on pins 2 & 3 of the chip also R42 was negative on one side and no output on the other (but had voltage output of around 2.5V). R43 was exactly 6.19K ohms as expected so that wasn't the problem. Decided to pull U37 and replaced with 14 dip dual in line socket and placed in new TL084 chip. Powered up, bong and then music - nice one, two down one to go.

Board 3 - also dead, exactly the same problems as board 2 except U37 was super hot.

I've had to order two DAC chips from Hong Kong to complete the boards - which are currently missing in the photos. I just kept swapping the good one from board to board.

The logic in the circuit is reasonably ok to follow, if you are an intermediate and have some skills in repair working, you just need a fair amount of spare time and patience to trouble shoot. From what I've seen the common problem has been U16, followed by a few others. I hope this helps for anyone with a dodgy sound board that they want to repair. Sheet 3 of 5 of the manual covers all the problem chips I encountered - maybe this part of the circuit is vulnerable (possibly from a voltage surge or something).

I'll help anyone, in need, if I can but it's difficult when the board is not in front of you.
 

Attachments

  • DSCF4550.jpg
    DSCF4550.jpg
    102.1 KB · Views: 66
  • DSCF4551.jpg
    DSCF4551.jpg
    104 KB · Views: 55
Last edited:
awesome work. lately people have been having trouble with MK1 sound boards I think lol

I also think action76 went ahead on one board and changed just about everything and it still wouldn't work. found that kind of peculiar.

you're officially in my awesome people list on here.
 
shame on me for putting off buying a $12 tool for so long.

Time to get a probe and fix some soundboards.

Great write up, glad someone finally decided to "get it done"
 
I've never even used my probe lol. it's ok, I'll wind up using it when I work on my other Defender boardset right?
 
awesome work. lately people have been having trouble with MK1 sound boards I think lol

I also think action76 went ahead on one board and changed just about everything and it still wouldn't work. found that kind of peculiar.

you're officially in my awesome people list on here.

I've repaired a lot of mk1 soundboards, but none recently. 90% of the problems have been associated with either a bad crystal (most common) or the amp. I'd recommend going to those after carrying out the usual checks for socketed chips, bent pins, traces, etc.

I've still got one mk2 soundboard that works for 5 seconds and then cuts out - intermittent problems are harder to trace, but in any case I don't have the U17 - gal chip. Specialist parts are virtually non existent here in the UK.
 
I've repaired a lot of mk1 soundboards, but none recently. 90% of the problems have been associated with either a bad crystal (most common) or the amp. I'd recommend going to those after carrying out the usual checks for socketed chips, bent pins, traces, etc.

I've still got one mk2 soundboard that works for 5 seconds and then cuts out - intermittent problems are harder to trace, but in any case I don't have the U17 - gal chip. Specialist parts are virtually non existent here in the UK.

I had a soundboard that would work for 5 seconds and cut out too and after I replaced the ribbon cable, the problem went away.
 
I've repaired a lot of mk1 soundboards, but none recently. 90% of the problems have been associated with either a bad crystal (most common) or the amp. I'd recommend going to those after carrying out the usual checks for socketed chips, bent pins, traces, etc.

I've still got one mk2 soundboard that works for 5 seconds and then cuts out - intermittent problems are harder to trace, but in any case I don't have the U17 - gal chip. Specialist parts are virtually non existent here in the UK.

I find the crystal normally only has to be replaced if it's missing and normally causes a 7-8 "bong" issue. I currently have one that has an issue that i've traced down to either u12/u13 as when any sound is played off those chips and all sound get played (that those chips have data for). the last one i have is an intermittent one which works fine after a minute or so but on first connection makes funny noises and doesn't always work as it should.

Things like the ribbon cable should be ruled out quickly and easily as they are very easily found and should be considered one of the first checks on the list of things that i believe most of us have mentioned more times than a record spins.

Jon thanks for posting this, and taking the time to trouble shoot. Its about time most of us got a logic probe and or started using it.
 
I had a soundboard that would work for 5 seconds and cut out too and after I replaced the ribbon cable, the problem went away.

Thanks for information Mike - it's not the ribbon cable because I've been using it to test the other boards with, but you have given me an idea.

Two of the pins on P4 aren't 100% straight, they're 'aligned' but there's a slight curve on them. I'll straighten them out completely and see whether that changes anything.
 
I had a soundboard that would work for 5 seconds and cut out too and after I replaced the ribbon cable, the problem went away.

You gotta be shi**ing me. My word, these boards are picky! The pin was curved by, and I'm not kidding, less than half a millimetre. I'd already sanded the pins down before (quite dull oxidation) and had just missed a small amount on the curved pin. Straightened them all out again (with a slightly wider spacing) and made sure all the pins were shiny - Bingo, up and running.

Great info - I'd already done this before, but this is beyond picky.
 
You gotta be shi**ing me. My word, these boards are picky! The pin was curved by, and I'm not kidding, less than half a millimetre. I'd already sanded the pins down before (quite dull oxidation) and had just missed a small amount on the curved pin. Straightened them all out again (with a slightly wider spacing) and made sure all the pins were shiny - Bingo, up and running.

Great info - I'd already done this before, but this is beyond picky.

Honestly there's a simple tool for straightening almost all the pins on all midway boards i've mentioned it in older posts. Another thing on the list of checks i do before even powering up a board and should be done by everyone.
 
Last edited:
Honestly there's a simple tool for straightening almost all the pins on all midway boards i've mentioned it in older posts. Another thing on the list of checks i do before even powering up a board and should be done by everyone.

what's the secret?
 
Honestly there's a simple tool for straightening almost all the pins on all midway boards i've mentioned it in older posts. Another thing on the list of checks i do before even powering up a board and should be done by everyone.

It's a small thin tube from a WD40 can - I remember that one. I've got something similar on a PCB cleaner can.

If you're going to buy a logic probe for this sound board, I'll give you a few pointers on what I do. Before I start, everything I know has largely been self taught. I'm an engineer, but not an electronics one. I know just about enough to be reasonably successful at repairing and won't know things like what the precise voltage should be coming from one component to the next.

Naturally, the use of the logic probe is best used after you've exhausted the usual inspection checks and swapped out socketed components, including you know the main board is good (note bent pins - even if you think you've already done this good enough the first time). It may identify something not working correctly or a broken trace, but it's quicker doing the inspection in my opinion. One thing to remember is never swap good parts into a non-working board. Always swap parts from the non-worker into the working board and test them that way (when in haste or tired you sometimes make obvious schoolboy mistakes). Have a decent volt metre to hand also.

1) You need a decent area away from the kids, etc. I know it's basic but if you're me I have to pull the test equipment from a cupboard and set up every time I do something and then put it away again (time consuming, irritating, etc). This doesn't happen often - I'm either ill or on holiday and both are infrequent. I've just been off for a few days, hence this thread - but I'm always popping into KLOV for a look.

2) I'm not sure what people know (sorry if you know this already). There are three lights on the logic probe. Green is LO (low state - ground), Red is HI (high state - positive voltage) and Yellow is PULSE (TTL or CMOS depending on the probe switch position you've selected). That is what is on mine, could be different on what you buy.

3) Print out the 5 circuit diagrams (A3 is good) from the back of the manual and get a green and red highlighter.

4) Ideally have two set ups. The first is a good working set up and the second is your problem board, that's two test rigs. This can speed things up once you think you've found something. Set up both test rigs with a logic probe each (because they're cheap, the test rigs aren't). Not to worry if you only have the one test rig, just swap you're known working board out with non-working having noted the outputs (by the logic probe) and voltages (by the volt metre) on your 'dodgy' component.

5) You can start at Y2 - the crystal should be generating a constant flash on the pulse without HI and LO. Now you know it is emitting something.

6) U17 at the GAL2 (on Sheet 1 of 5) is a good place to start. The chip is 24 pin and should be working with any luck. The pins are numbered - identified from a small (usually semi-circular) indent at the top of the chip (sorry if you know this). With the indent facing up, pin 1 is top left down to pin 12 at the bottom left. Pin 13 is then bottom right up to pin 24 top right. Inputs are 1 to 13 (IN 1 to 12), without pin 12, but 12 may be grounded and it still mat have a state of HI or LO. Check the pins 1 to 13 those on the entire left hand side and bottom right pin. All pins on these DIP components are numbered in the anti-clockwise direction (1 starting at the top left to whatever at the top right). You can print data sheets off for individual components if you like, but I usually use my working board as a bench mark. I think pin 1 on U17 is the clock out and should be giving the stable flashing light on pulse. All the other pins should light the probe like a Christmas tree, all lights flashing. Logic is feeding in. Now check outputs. Outputs are pins (14 to 23). If these are lighting the probe up like a Christmas tree logic is being transmitted out - GAL2 is 'operating'.

7) Mark the 'pins' on the printed sheets with your green highlighter. You've guessed it - green for good, red for 'possibly' bad (see parallel circuits later on).

8) U35, U36, U21 and U22 are usually a good place to start next, follow exactly the same process as in 6) checking the inputs and outputs. If these are good keep following the logic path - U32, U33 & 34. Ticking them off the printed sheets as you go.

9) You could just start at U38 on sheet 3 of 5 checking pins 1 for input and 2 for output and then move onto U16 (the DAC) which seems to be a notorious trouble maker. Remember the VOUT on pin 9 of U16 generates no logic pulse - you'll need the voltmeter past here and your good board.

When components are working in a parallel circuit you can get misleading results. The best advice I can give is - if you find something not quite generating the correct responses, check everything leading up to and out of the component and everything within the parallel circuit - even then you may miss something. Check responses and voltages against your working board. All things in the parallel circuit can affect all other parts in that circuit. Remember series and parallel circuits from physics lessons?

I hope this helps a little - it does take time, patience and practice but you will improve over time. If I can do this there's no reason anyone else can, it depends on your patience and effort levels. It also requires some self restraint, at times, you may know what I mean once you start . I haven't covered everything, something else could be at fault (capacitor or SIP?) but at least this is some information on how to test the logic components.

GOOD LUCK - let me know if you take the plunge and what your set up is.
 
Last edited:
Awesome, thanks again john!

yup the spray can extension (canned air ones are best as there's no leftover residue)

It'll take a couple weeks but i'll definitely keep you updated.
 
Back
Top Bottom