[sdiy] seek help on Jupiter 6 repair

[Anderson, Robert O]

I have a Roland Jupiter 6 that I received in need of repair.  On power up
the tune light is on and none of the buttons do anything.  The LEDS in this
condition indicate a pretty standard voice setup.  Now if I momentarily
change to jig position all the buttons begin to function by illuminating
their respective LEDs.  Thus, it seems that the processor board is working
to some degree.  The tune LED still remains on and no program number LED is
illuminated.

I tried the A-1calibration to zero the DAC offset on each of the boards.
They were only slightly off and a small adjustement of the trim pot nulled
the offset.  The calibration procedure then says that the tune LED should
extinguish after a few seconds..  Unfortunately it remains on.  Power supply
voltages and battery voltages are ok.

The volume and tune pots look damaged.  I would assume that the signal used
in the tuning process comes before the volume pot.  Also, I assume that the
tune pot is used in the tuning process.  If these are the culprit I'll
repair them at once, but I want to minimize removing the boards.

I only have the schematics for the CPU board but not the voice or panels.
Does anyone have any experience with the Jupiter 6.  Is there any way to
know where the tune is getting stuck, i.e. voice number.  Anyone have
schematics for the rest of the boards?  Any advice humbly appreciated.
Thanks

Bob A