[sdiy] SH-101 help

[patchell]

    I am helping a friend fix his SH-101.

    #1..Is there a copy of the schematic on line.  Every link I have
followed for a schematic has ended in a dead end.. :-(

    #2..Symptoms: The instrument seems to work except for when you press
down a key, the pitch does not change.  But this action does generate a
trigger.  When an external CV is pluged in, you do get a pitch change.
The CV out, however, is stuck at the same voltage level no matter which
key is presses.

    #3...What I do know...I managed to trace the pitch CV a bit.  The
SH-101 has a very crude DAC made out of resistors and a CD4050.  When I
look at the output of the "DAC", I can observe everything working here.
Tracing further down the line, I get to a Sample-Hold which does vary in
voltage as you press the key.  The hold capacitor then goes to a TL062
dual opamp.  However, this is where the voltage gets lost.  While I can
see the keyboard voltage on the + input to the opamp, the output and the
- input, which seem to be connected through a 1K resistor, are stuck at
a negative voltage.  Off hand, I would say that this opamp is bad,
however, something else could be dragging it down.

    Does any of this sound familiar to SH-101 experts?  If nothing else,
I will try changing the opamp out tomorrow, but, in my experience,
opamps almost never fail...so I suspect a different problem.

--
 -Jim
------------------------------------------------
* Visit:http://www.silcom.com/~patchell/
*-----------------------------------------------
*I'm sure glad Merry Christmas comes just once a year
* -Yogi Yorgensen
------------------------------------------------