26 Sep 2018

Mutant Fighter - Data East 1991 (repair log)

Game took very long time to boot, then would play extremely slow, sometimes hanged, sometimes played overspeed for a second, and also had no sound. Otherwise board was in very good condition like it's never been operated:


I started by troubleshooting sound issue. First obvious thing I noticed was sound RAM @ J24 was a shiny one. Piggybacking a known good RAM on top of it restored sound. I replaced it and that was all that was needed in the sound section.

Then the second issue regarding speed of play, hanging, overspeed. Quite weird. I probed main CPU (68000 CPU in a custom QFP package marked '59') for a dodgy RESET or CLOCK signal: nothing to mention here. Then I found by touching a specific area of the board on the solder side I could get the game to play at correct speed for a second, and by doing so every second I could have the game playing normally. I thoroughly inspected the area and found a factory defect: one of the leg of the LS74 @ K3 wasn't soldered. I had the impression that by applying pressure on it game would play fine.


I resoldered it but nothing changed. Thinking the chip could be bad and not having the possibility to test it on board with my logic comparator because of it being SMD, I took the decision to replace it: no dice.
To me there was clearly a floating signal somewhere and by touching the concerned trace/pin with my hand I could restore the connection or at least drive the signal to a state where the board would be happy with it. I quickly found a floating trace, that lead me to an other LS74 @ J5. This time chips seemed soldered properly but by using my magnifying lamp I could see one of its legs was covered in solder, so as the associated pad but there was a really tiny crack in between. I tried to reflow the leg but solder was stubborn and didn't want to adhere to it. I had to add quite a big blob of solder for it to adhere on both the leg and the pad:


This time game played normally:



Game fixed.


2 comments:

  1. hi from greece ..may coming a bonantza bros for repair ..have some questions..the floppy drive is the same with computer ?the floppy disk is like normal 1.44 or different?and if this is ok how can transfer the img file from pc to fdd just copy or need something different ??thanks allot for your time..mail is limpitakisb@gmail.com thanks for your time

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    Replies
    1. Hi,
      Yes floppy drive is similar to a computer one however some people have reported not all work with S24. Floppy disk is a standard hi-density 1.44MB with a specific formatting. Transferring an img file to fdd is nearly impossible with modern computers.

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