Discussion about the Korg PolySix synthesizer

Hello there,

my Trident MK2 is defective.

Symptom: VCO 1 is defective for one voice.

Up to now I was able to found out: Input 1 of IC704 (4x CMOS switch) on
KLM-379 doesn't get the VCO signal on voice 7. On all others it does.

There are some oddities with op amp IC707 but I'm not yet sure. The
schematics and the circuit board design hint to the direction that IC707
"feeds" IC704.

The IC707 is a 4558, I assume that it is similar in the Polysix.

Did anybody of you experience a similar problem? What about replacing
the 4558, did this help?

Furthermore, some of the 4558s carry a date stamp of 1997 which means
they must have been replaced by an earlier owner.

Unfortunately there is no shop selling electronic parts in reach so I
can't just go for it and try replacing it. Mail order is an option but
not for a few ICs...

Thank you for commenting.

Best,

  Niels