[sdiy] Weird Prophet 600 issue

[Travis Thatcher]

A friend and I have been trying to get our buddy's Prophet 600
fully functional.  He got it at a pawn shop with a blown battery which
my friend replaced, recapped the power supply and replaced a cap that
blew up near the DAC.  It stores patches and all switches function
however only the right half of the pots have any effect (everything on
the smaller tan pcb).  We started probing things with a scope and
traced around U107 - the 4174 Hex Latch. The chip in there was
a CD40174 and we replaced it hoping that could help but no dice. We
noticed that pin 7 and pin 10 are the enable signals for the mux for
each pcb with the controls. The duty cycle for the mux on the right
board is way wider than the duty cycle for the one on the left board
so I swapped the signals thinking that maybe the enable signal was
stuck only enabling the one side. This didn't fix anything but
curiously when swapping those
lines via alligator clips when the synth was on some params from the
left board were written into RAM. I assume it was the mux kinda
freaking out for a second during the disconnect but once the wires
were connected the left side was still unresponsive. I'm wondering if
its the MUX that is bad or if there's something else we should look
at. Curious if anyone has a P600 and can check the waveforms at pin 7
and 10 of U107.

-- 
http://www.travisthatcher.com
http://www.soundcloud.com/thevoiceofsaturn