Mortal Kombat - Resetting

xrodney

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Hi

i just bought a mortal kombat cabinet. it works fine for about 10 minutes, then it resets it self. then after 1 or 2 minutes it repeats the resets. what can be the problem? is it a power issue?

regards

Rodney
 
could be a power issue. could be where it drops enough below 5 volts at certain times, and that could cause your resets.

verify that you're getting about 5.15V at the JAMMA edge. your power supply could also just be on the outs too. ever have problems getting the game to boot at all upon power up?
 
What do the power on self tests show? Do they indicate any bad chips?

Power supplies can fail in different ways. Some ways are hard to check without taking extra steps.

1. Is the voltage level set to 5.1v when measured at a chip on the board? You want to check this AT the board since there are voltage drops in the wiring harness.

2. Does the voltage stay steady or does it fluctuate? If it fluctuates (beyond a couple hundredths of a volt) then replace the supply.

3. Is the power output noisy? Really the only way to truly check this is with an oscilloscope if you have a switching power supply. The switching frequency is too high for your voltmeter to really show what's going on. You CAN eyeball the power supply and look for ruptured capacitors - ones that have split open the seams on top or busted out their guts from the bottom. If this is the case, replace the caps or the whole power supply.

You can check output noise on an analog power supply with a voltmeter. It just doesn't work well to check it on a switcher using one.

RJ
 
I forgot which legs on a chip you use to test for voltage. can you, for the audience, tell me how to do that? lol (isn't it the first and last pins on the keyed side?)
 
For most chips (TTL logic, EPROMs, and SRAM) you put the notch of the chip to the left so pin 1 is bottom left.... Then you put the ground lead on the bottom right pin (pin 14 on a 28pin EPROM) and the +5 on the upper left pin (pin 28 of a 28pin EPROM)...

RJ
 
mine does the same exact thing, and the issue comes from the jamma connector that seems to be just a tiny bit loose. After a couple of weeks of intense play, i get the same issue you are describing, i just remove the connector then replug it back in, and its fine for a while again.

Try it! you never know!
 
funny you mention that, I've told several stories about those Midway JAMMA harnesses having pins that just fall out of the harness. on my KI cab it happens with the P2 inputs and on my MK cab I had to redo the entire video section on the JAMMA harness.

MAYBE you just have an intermittent +5. it's the smaller section of the harness past the white key, the red wires are +5, yellow +12, black Ground, and I forget what the -5 is, it's either white or green or blue or whatever. :) just pop the harness off and try wiggling those around, if they move, then you've found the potential culprit.
 
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