Archive of the former Yahoo!Groups mailing list: Discussion about the Korg PolySix synthesizer

IC9 pin 2 should be at 0V all the time.  If you have a waveform at pin 2, I
would replace IC9.  Also, your photos say 0.5V/division.   Are you using a 10:1

scope probe?  If so, maybe it's really 5V/division?   That would make the waveforms

closer to what I would expect, if you are playing 5 keys that are each an octave

apart.   That's a better test at this pt than playing keys that are together on the

keyboard.

Are you saying that the waveform at IC9-7 does not change when you press keys?

Press 5 keys that are adjacent on the keyboard and look at IC9-7, then press

5 C keys that are octaves apart.   In the second case, the steps in the waveform

should be about 1/2 volt apart.

    Actually the waveform at IC9-5 looks OK to me, assuming it's 5V/div and

not 0.5    You are not triggering the scope properly, though, since we can see

a hor line through the waveform.   It will be easier to trigger correctly if

you can get the waveform to fill more of the screen.    Then play with the trigger

level.    Use normal trigger mode, not auto.  

You need to sort out whether your scope probe is 10:1 or not.   If you can get to

0.5 volts per division, it should make the waveforms easier for us to look at.

(I suspect you may be at 5V / division currently). 

Anyway, it is starting to look like IC9 may be bad.   If you decide to change it,

the preferred method is to cut each lead close to the body of the chip.   Remove the

body, then heat each lead individually from the top side of the bd and pull out the

lead.   Check first to see if any leads are bent underneath, as the corner ones often are.

You may have to straighten them before they will come out.

 Put a socket in for any new chip you install.   They are cheap, and on these old circuit

bds, you may only get one chip change per location before the traces start lifting up.

    Bob