Mortal Kombat board repair

Jon Hughes

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We had a 4 day holiday in the UK with the diamond jubilee and it's raining so I had some spare time. I decided to have a go at repairing some boards I bought some time back, way back and thought I'd share the findings.

I started repairing from self learning and studying various sites. I've made a mess of a few boards in my time while not having the correct equipment. You often learn from your mistakes, but I believe it pays to think things through before attacking boards with a soldering iron....

First up is a memory expansion board from Mortal Kombat 2. I think one of the previous owners got a little frustrated with it and the pictures show what happens when you lose patience - 120 bent pins on the P14 & P15 connectors. Also noticed U4 socket had been replaced with a DIL socket with a 20 pin chip installed. Removing chip U4 I found a bent leg on pin 11 (but this didn't really matter in the end).

Photo 1 the board in question.
Photo 2 & 3 the rats nest of bent pins.
Photo 4 my set up for de-soldering.
Photo 5 pin 11 straightened on chip U4.
Photo 6 nice new connectors
Photo 7 board populated
Photo 8 short pins mean the boards touch, but the originals are impossible to find.
Photo 9 RESULT!

If you can carefully look at photo 6 you may see the chip at U4 is a SN74LS244N. After investigation I found out it should match U3 & U5 and be a 74ACT0244. Luckily there is one at UD22 on a T-unit board. Desoldered UD22 from my donor board and placed it in correctly as shown in photo 7. I wonder if someone had attempted at a have a go repair at this board.

Total repair time 4 hours - would have been a lot less but the new connectors would not fit into the soldering eyes unless they were perfectly free from solder - biatch.
 

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Next up is a Mortal Kombat T-unit board. It looks like the previous owner attempted to convert this to a Mortal Kombat 2, T-unit. I'm not sure how things would have turned out for the conversion, since the memory expansion board has pins (male) on the connector and the would be convesion was also putting pins (male) on the T-unit.

Anyway, I like Mortal Kombat so I decided to put it back how it was.

Photo 1 the board in question
Photo 2 messed up male connectors at P14 & P15
Photo 3 horrible solder attempt at P14 & P15
Photo 4 solder contacting adjacent pins
Photo 5 ALL GONE!

The solder had been applied in haste and was connecting at least 2 pins at 4 positions. After removing everything and populating the board, it initially couldn't find any of the ROM chips through UJ12 to UG22 - all red. After prodding around with a logic probe for about an hour and finding no problems with inputs and outputs I finally gave up. Decided to plug it back in to the cab and see what was going on and to my suprise it worked fine. Something metallic did fall off the back of the board part way through and it may have been causing a short circuit, but ended in RESULT! I think I've been fairly lucky with both these boards. Total repair time 3 hours.
 

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nice write ups, and nice workstation as well. I couldn't begin to tell you how many bent header pins i've straightened in the past year. (the red nozzel for canned air works amazing for this). And the same with pins on the solder side (they're always mashed down onto the board or another leg)

oh and i must say DAMN wtf did the previous owner of that board do to those header pins....
 
Thanks for the comment. Yes the pins, it's not like they're bent over to one side - they're twisted together. Not an accident I think. I know 20 pin chips look similar but placing that chip at U4? I hoped the thread would help first time repairers, like I was once, not to hack what are possibly perfectly good boards with very minor issues.
 
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