Vintage Synth Repair

Hi Malte,

Thank you for the help so far! I figured I should reply back when I had something useful to add.

I actually got sidetracked with the original issue above. The main output began to fail. I tracked it down to a faulty diode and transistor on board C. (The manual showed a 5172 but this had a 2SC828 in it).

This is a three bus black MKI but there are no CV I/O mods on it yet. I plan to put them in after this is working again. In order to apply CV I've often disconnected the keyboard and have applied a voltage directly to C6 on Board A-1.

As it turns out, you were correct! Q7 was failing. I replaced it managed to get rid of that problem. Unfortunately that revealed an underlying issue :(

Now when one releases the key, it hangs and tends to lift up by a semitone or so. If I set the output to the main VCA - AR - it will remain audible endlessly. If I set it to ADSR, it can fade away (though I believe the signal is still passing though up to that envelope. The ADSR just happens to hide the signal by fading it out).

Ugh.