Korg Mono/Poly

Hi Chase

> should which is creating the noise. So now I am changing the
> capacitors, op amps, and voltage regulators and if that does not work,
> then I am out of ideas.

You might try to isolate the error also by disconnecting some boards,
and measure the rest:
'+++' means switch power on
'---' means switch power off

disconnect all boards
+++
check powersupply out with oscilloscope
---
connect KLM-356 (uP board) to powersupply and keyboard to KLM-356
(perhaps also the 353 with the keyboardmode switches is required)
+++
check the CVs at the connector pins 27-1 to 27-4 with oscilloscope
---
connect the VCO-board
+++
check the CVs at the connector pins 1,3, 9, and 11 of IC-7 with
oscilloscope.
check the outputs of IC-22 (opamp after Ext VCO in) with oscilloscope.
check at the four summing points for VCO-CVs
check the output of all four VCOs separately.
---
add VCF board
+++
Check again the output of the VCOs

and so on....

If the constant FM appears, the let the constellation as it is, but go
back in the measurement chain to check how far 'back' the FM can be
traced (e.g. already on VCO board, but not at the uP-board-output).

I don't remember wether the ICs originally are socketed. But if they
are, you might also remove some relevant ICs.

Florian