Hi,
I have an issue with my Yamaha SK-20. Well a couple actually.
The first issue is that the Strings signal is audible in the Polysynth mixer output.
To explain a little better, there is a mixer section for Organ, Strings, and Polysynth before the Master Volume and main output. When the String section fader is set to its minimum it can still be heard through the Polysynth section. So when I have the Polysynth fader up and play the keyboard, the Strings section can be heard underneath the Polysynth output at a low volume. It also appears to overdrive the output so that it slightly distorts.
The bleed occurs only on the Polysynth mixer slider. If I set the Polysynth so that it outputs nothing (ie. ADSR all set to 0, filter set to lowest, etc.) and set the Polysynth mixer slider up and all the other sliders down, when I depress any keys I can hear the String section coming through the output.
If I do the same with the Organ section, the problem doesn't occur.
I checked the volume pedal input on the rear of the synth. There's some strange behaviour going on. I plugged in a Roland EV-5 foot pedal and at first it altered the volume of the respective sections (String or Mixed). Then it ceased affecting the volume. There was a smell of solder/component burn coming from the synth (which may or may not be caused by this - the same/similar smell came from it last night too).
Now when the volume pedal is plugged into either of the pedal input jacks, the respective sections are muted. Very odd. It has no effect other than muting the section whose input it is in. Adjusting the trim on the pedal does nothing.
I opened up the synth and took out the JK board but it looks fine. No obvious damage to either of the ICs and the caps all seem to be ok.
The second issue is that the transformer started smoking after having been plugged in for a while. The synth wan't powered on when this started happening, but it was plugged in. This is likely the origin of the smell of burning I experienced.