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Repair Logs

Mario Bros (Nintendo) PCB repairs


Tools: Schematics, Logic Probe

Problem: Walk sound distorted

Both Mario and Luigi walk sounds were messed up. Sounded more like a gush of air than the normal walking sound. Locating the Walk 1 and Walk 2 circuits on the schematics, it shows both LS629s at 1J and 2J do most of the work. Replacing both of these chips fixed the walk sound for both players.

Solution: Replaced bad 74LS629 chips at 1J and 2J on the CPU board


Problem: All background graphics shifted up with the score barely showing on the bottom of the screen.

My first though was this was a Video board problem. I probed around the LS86 and LS377 and noticed that if I shorted pins 5 and 6 of the LS86 at 1D, that the picture would shift down to close to where it should be. Pin 6 is an input from the FLIP circuit and was stuck low, if I pulled this pin high with +5, the background would shift into place. Tracing back from pin 6 on 1D, All the chips were acting as they should. I moved then to the CPU board side of the FLIP circuit. On the CPU board, FLIP is connected first to pin 12 of the LS04 at 1H. Probing that pin, I noticed that it was LOW, I followed this trace back to the Video board where it connects to pin 9 and 10 of the LS00 at 5H. I turned off the board and check for continuity and sure enough it was open. Moving back to the CPU board, the trace leading to pin 12 of the LS04 at 1H was damaged. Repairing that trace fixed the problem.

Solutions: Pin 12 of LS04 at 1H on the CPU was out of circuit, repairing the trace shifted the screen back to normal.


Problem: Analog sounds OK, digital sounds barely audible

Tools: Soldering Iron, Solder Sucker, Flush cut snips

Game plays well, but could only hear walking sounds of Mario and Luigi. At first I thought the digital sounds were completely out, but realized I could barely hear the digital sounds. At which point I thought it might be the digital amplifier. So I replaced LM3900N at 3M and digital sounds are back to normal.

Solution: Replaced LM3900N at 3M

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