[sdiy] Polysix does not save settings

[Michael Buchstaller]

Hello list friends,

recently i got a dead polysix for cheap.

Externally, it is in medium condition (wood scratched, but all keys
OK and all knobs exist).

Internally, it was a total mess. Someone who does not know which side of
a soldering iron gets hot, tried to repair it. Nearly all pots on all boards have
been desoldered and soldered in with large blobs of tin.
Two of the power supply transistors were blown, and various shorts due to
the large amounts of solder where all over the place.
At least all the SSM chips are in there.

After cleaning up and fixing the P/S, it seemed to work. But all pots have been
turned to zero, so i had to re-calibrate everything according to the service manual.
Had to do this several times, to get a useful approximation to the correct values.

The battery had to be replaced, too. (began to leak, but did not make large
corrosion on the board).

Now, it works and i can play.

But 3 things are not working:
1. The effects unit does not do chorus, only the two other settings.
   This is not a bug on the effects board. The TTL signal that enables the
   chorus remains zero regardless of the panel switch.
2. The octave select switch has no effect, but in manual mode it works
3. I cannot write patches into memory. if i do, that bank contains data junk.
   Loading factory sounds from tape (sound card, of course) does work, so
   i suspect it is not a fault with the processor/RAM/battery circuitry.

Looking with a scope on the data lines connecting the front panel to the
KLM366 board shows that all signals are alive at TTL levels (0.1 ... 4.2 V),
only line P13 is weak (0.2 ... 2 V) - I suspect that this could be the reason for
my troubles.
Tracing this line though the schematics, i goes to a bunch of diodes in the
control panel. How can i find out where the fault is ?

Did anybody experience the same ? Any common points to look at ?

Thank you all !!


-Michael Buchstaller