Hi Daniel,
Yes, the volume pedal is the wrong type, but the difference is only that the pot is a different value (10K instead of 50K) and the tip/ring wires are reversed. I'm not sure if that's the culprit for the smoking transformer which is quite troubling.
Judging from the schems, the power switch should stop all power coming into the synth. But the issue is that the transformer is receiving power when the switch is off but still plugged in. Which is very strange and, in this case, dangerous.
Cheers,
Karl
On Sun, Feb 26, 2017 at 11:19 AM, Daniel Forró danforcz@... [vintagesynthrepair] <vintagesynthrepair@yahoogroups.com> wrote:
Your previous mail came, too...I have SK20, do repairs of my equipment, but my instrument is OK so there was no need to open it and start to work on it. I also didn't study Service Manual more deeply. So I'm afraid I can't help much...The only thing I can say is that Roland volume pedal has different connection, different pot inside, so generally it's not recommended to use it for Yamaha instruments (or Yamaha FC7 for Roland instruments - when I wanted to use it with my Roland V-piano, I had to change internal connection).I'm not sure, but maybe this could cause some problems you describe.Daniel ForroOn Feb 26, 2017, at 4:58 AM, Karl Knuttel pinksoir@... [vintagesynthrepair] wrote:Hi,
My SK20 is exhibiting strange behaviour.
The first issue is that the 'Strings' section signal is audible in the 'Polysynth' section 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. There's strange behaviour there. I plugged in a Roland EV-5 foot pedal and at first it altered the volume of the respective sections (Strings or Mixed). Then it ceased affecting the volume. There was a smell of solder/component burn coming from the synth. There was a similar smell emanating from the synth last night when I was checking it as well.
So now when the volume pedal is plugged into either of the pedal input jacks, the respective sections are muted. Very odd.
I opened up the synth and took out the JK board but visually 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 now seems to be overheating. I left the synth plugged in but powered off and the transformer began to smoke and there was a smell of melt coming from the area.
Any help would be greatly appreciated. Here is the service manual: https://elektrotanya.com/yamaha_sk20_synthesizer_sm.pdf/download.html
(Apologies if this is a double post - I posted directly to the group but it didn't seem to go through)Cheers,Karl