Vintage Synth Repair

In a message dated 4/16/04 3:21:54 AM, ferrograph@... writes:

<< yes- I had the same thing in a monopoly a few years ago. took me a while 
to 
figure it out.... look for the oscillator chips themselves; they will have a 
thermistor device glued to the top of them. the glue is supposed to keep the 
devices in close contact but eventually goes off & cracks, leading to freq 
drift 
instead of temp compensation. >>

As far as I know, the Polysix does not have oscillator chips, per se.  At 
least not in the sense that the MonoPoly does.  The MonoPoly has four SSM 2033 
VCO IC's.  The VCO's in the Polysix are made from opamps and discrete 
components.  The MonoPoly VCO's had exponential response, whereas the Polysix has linear 
response VCO's.  

Because of its linear VCO's, the Polysix has a fairly unusual and complex 
system of modulation CV distribution.  (I won't go into the reason why at this 
moment, sorry).  Nevertheless, it is very likely that the aforementioned Polysix 
problem exists somewhere in the modulation CV multiplexing circuitry, and not 
in the individual VCO's themselves.  BTW, the Polysix VCO's are not 
temperature-compensated.  That is, they don't have the thermistor of which you speak.  
The fact that they are linear VCO's makes them much less vulnerable to 
temperature effects than exponential VCO's would be.

Unfortunately, I don't have the Polysix schematics handy at this moment, so I 
can't offer any more advice.

Michael Bacich