Mortal Kombat 2 Sound Board repair

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Does anyone have a document or know of one for troubleshooting and repairing the reset section of a MK2 type sound board? If not, any advice would also be appreciated.

Thanks.
 
Does anyone have a document or know of one for troubleshooting and repairing the reset section of a MK2 type sound board? If not, any advice would also be appreciated.

Thanks.


I would like help also, I have MK1 sound board I can't figure out!
 
i don't know of anyone who repairs them, i'd say throw it in a parts pile and pick up another sound board off ebay.
 
Other then the manual (http://www.crazykong.com/manuals/MortalKombat2.man.pdf), I could take a whack at helping you. What's the problem with it? Perused the schematics, PDF Page 72 has the sound board's main overview. RST is hooked up to.. Two Flipflops.

Oh, wait. Page 76 details the reset circuits themselves. User Reset and Power-On Reset. Looks really simple. Hex Inverter and Schmitt Trigger on Poweron Reset line, User has NAND Gate and Schmitt Trigger. 4.7k Pull-up for biasing.

Sorry, rambling. So describe your problem, what's the thing doing?
 
I don't think the CPU is ever booting. I am not great at logic stuff but at looking at the schematics there is a hard and soft reset and it looks like that one should be high and one low for the cpu to boot. Both of them on mine stays high. I may be totally off with that thinking. I guess I need to figure out what part is failing to cause this.

Thanks for you help by the way.

Other then the manual (http://www.crazykong.com/manuals/MortalKombat2.man.pdf), I could take a whack at helping you. What's the problem with it? Perused the schematics, PDF Page 72 has the sound board's main overview. RST is hooked up to.. Two Flipflops.

Oh, wait. Page 76 details the reset circuits themselves. User Reset and Power-On Reset. Looks really simple. Hex Inverter and Schmitt Trigger on Poweron Reset line, User has NAND Gate and Schmitt Trigger. 4.7k Pull-up for biasing.

Sorry, rambling. So describe your problem, what's the thing doing?
 
When powered up, your reset line should unlatch. Check the output of U38 Pin 4 (http://www.nxp.com/documents/data_sheet/74HC_HCT14.pdf). If it's high, reset is held up for some reason.

Check the logic output of U38 Pin 6, if it's high, Reset is asserted. Then check Pin 4. If this is also high, then U38 is bad, because U38 is an inverting trigger, and pin 6 is fed into pin 3 (which is inverted on pin 4, and should be low if pin 3/6 is high). U38's inverting capabilities are used all over that circuit, so that'd explain the nonsense.

The RESET with a line over it is Active Low. Reset without the line is active high. The whole stupid reset circuit is a Wired OR Gate, and it took me a minute to understand it. Heh.

Do check pin 9 though. When the unit is on, pin 9 of U38 should go High to start the reset unlatching (R20 and C3 are a RC Timer circuit, cap charges to delay the reset unlatch to whatever that time constant works out to.)

Hope this helps.
 
Thanks for the info. I think what you described is exactly what is happening. I am going to test it again to make sure. I will probably swap out the U38 anyway just to be sure. I hope I can find one around here. Looks like a 74HC14. I would like to find it locally so I can go ahead and try it, but I may have to order it. Thanks, I keep you posted on what I find out.
 
this is completely over my head right now lol

i've never used a logic probe i suppose i should start.
 
Well, I was wrong the logic on the U38 all seemed to be correct. Pin 4 was high but pin 3 and 6 were low. Pin 9 was high. I am thinking it might not be the reset section after all. I will give you the status of the pins on U38 in case you see something wrong.

Pins
1 L
2 H
3 L
4 H
5 H
6 L
7 L Ground
8 L
9 H
10-13 NOT USED
14 Vcc

The reason I thought it was the reset section (and it may still be) is that the LED never comes on and it doesn't bong at power-up. I figured the CPU was not getting the signal from reset to boot. My other thoughts were the CPU itself may be bad or the crystal is bad but I am not sure how to test the crystal w/o an oscilloscope. What do you think?
 
Pin Groups:
I/O
1/2: Correct
3/4: Correct
5/6: Correct
7: GROUND
9/8: Correct
10-13: Spare Gates
14: VCC

Looks like logic is ok. 4 High 6 Low means reset is unasserted.

I'd swap CPU's and see what happens, if you're not getting the BONG! at startup.

Crystal sadly can't be tested without an O-Scope or Frequency Counter (Some DMM's have them.)
 
Well I don't have another CPU to try but I did find a DMM with a frequency counter. It is supposed to be a 10Mhz crystal so I set the meter to Mhz and read the crystal with the board powered up and I got very low readings that fluctuated from 0.12 to 0.34 but no where near 10.00 where I believe it should be if I am using this meter right.
 
If the DMM supports reading up that high on it's frequency counter, then yes, your crystal isn't putting out 10Mhz. It's putting out 12-34khz. Check power to the CPU to make sure it's getting proper voltage. If so, you may be on the hunt for a new Crystal.
 
Yeah, I have tried to find a replacement but I can't find which 10 MHz crystal to get. I can find 10 MHz xtals but they have different tolerance ratings and load capacitance and frequency stability. I don't know if this stuff matters or not. The xtal on the board has 10.000
KDS 9L
Japan

I can't seem to find a match. If you have any ideas let me know.
Thanks
 
Thanks a million dude. I will get a replacement and see what happens. I will let you know the results.
 
OK check this out. I think I was testing the xtal wrong before. I thought one lead went to one side and the other went on the other side. I researched it and black goes to ground and red to a lead. This method gives a 10.00 on one side and a 00.02 on the other. I assume this means the xtal is good unless I am supposed to get a 10 on both sides. The really interesting part is when I test the crystal the LED that NEVER comes on does and stays on just like it is supposed to. I still get no sound but, apparently something to do with the meter on the crystal causes the logic to turn the light on like it should. What in the world do you make of this?
 
Sounds like your meter could be loading the crystal's circuit when you test is like that. Check the capacitors pre and post crystal. Honestly, I'd be taking a crack at your CPU at this point to see if it's bad, if the caps don't show any promise.

Also, the Peizo effect from the crystal will only oscillate out the side it's being "Pinged" from, which would be correct then that you're getting 10.0 out one side and nothing on the other (as it's ground).
 
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Been a while since any updates but I had to take a break from this an d work on something else. I changed the tiny 20 pf(i think not looking at schematics now) caps on both ends of the crystal and no change. I guess it has to be the CPU but I don't have a spare and haven't had much luck in locating that part to buy. Is there any way to test the CPU?
 
Well I was able to locate a CPU replacement for the board and of course ther is good and bad news. The LED on the sound board now lights up a couple of seconds after startup and stays on like it should so apparently there was something wrong with the CPU. However, I am still not getting sound..no startup bong or anything else. WindDrake, I hope you are still subbed to this thread and get this. Let me know if you have any other ideas.
Thanks
 
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