[sdiy] Weird Yamaha CS40M problem

[Adam Inglis (synthDIY)]

> On 18 Sep 2021, at 7:34 am, Antti Pitkämäki via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> The pitch of the strange oscillation changes when changing filter cutoff frequency, and it ends if the filter cutoff frequency is changed considerably. Also turning down the resonance ends the weird oscillation, after which everything works normally.

Antti, a couple of thoughts:
• there’s no garbage anywhere on the filter PCB, you’ve cleaned, inspected etc etc?
• have you been through the calibration procedures for the filter ? (around page 47 in the SM you linked) How does it respond? 
• you say there are very specific conditions for the oscillation to start: set those conditions up and examine the VCO and MOD boards as well with your scope. It may seem like it’s the filter board but as you say, unlikely both filter circuits would be faulty…

A


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