Vintage Synth Repair

In a message dated 8/9/05 1:27:08 AM, Bakis Sirros 
<synth_freak_2000@...> writes:

<<he made all the mods but obviously he made a mistake(
a short sircuit occured somewhere during the
modification works probably) and one(or more?) of the
chips of the SEM board has been broken. the result?
now, with no patchings at all in the SEM's newly added
patchboard, the lfo constantly modulates the pitch of
both vco's. >>

You probably do not have a bad chip.  Your problem is probably a result of 
incorrect wiring of the modification.  Your tech needs to check his work again, 
and very carefully.  There is, however, one chip that can cause this kind of 
LFO modulation problem -- It is A23 on the main board.  It is an LM3080A IC.  
Be careful with this chip.  They are very hard to find these days.  Again, the 
chip is probably OK, and your problem is more likely due to incorrect wiring.

Michael Bacich