Actually, IC39-3 is a virtual ground node due to op amp IC19, so it should be sitting
at 0V all the time. My mistake. But how about pin 7 of IC 19? This is also called
TP2. If pin 3 of IC31 is sitting at -10V, then the outputs would probably be at that
voltage, as you have said before, so maybe that chip is OK. IC9-1 should have something
like 5-8 different voltage levels if you hold 5 notes. According to the schematic, it's about
0.5V / octave, so you should be able to see this voltage changing as you play
different notes. The total time is divided into ~8 different time slots, and the voltages
for the 5 notes are each assigned to one of these time slots. If you play low C, then the
next C up, then the next C, etc, until you have 5 oscillators on (use hold mode for this)
than at IC9 you should see 5 levels, each 0.5 volts apart. If you play the notes in
ascending order, I think you may see a stair step pattern at IC9-1 with the voltage increasing
0.5V each step, then jumping back down at the end. There will be a couple of other levels
in there as well, but you should be able to see 5 levels repeated which correspond to your notes.
If you don't see that at IC9-1, then maybe check each output of IC7 and 8 for good digital levels.
IC9-1 should be -10.7/10 times whatever you have at IC9-7 with ~5V added to it.
From: "mpe1969@tpg.com.au [PolySix]" <PolySix@yahoogroups.com>
To: PolySix@yahoogroups.com
Sent: Monday, May 4, 2015 7:12 AM
Subject: Re: [PolySix] Re: Key assign mode issue
Thanks, I had another look tonight. I tried to upload some oscilloscope photos but they didn't seem to save to my album.
IC9 has a dc around -2 to 2.5v that rises to about -0.5 then drops to around -4v then returns to around -2.5v. (as a pattern) I took some photos..... Hitting keys does not seem to influence this pattern
Ic39 (the one above ic31) does not have anything happening on pin3. IC31 has -10v on pin3.
I was about to replace ic31 but thought I would hold off as ic9 doesn't seem to be doing what you described.
Will try again with the photos!
Thanks again