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.
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