Discussion about the Korg PolySix synthesizer

Hi again,
    Now I am thinking that the gate LED's staying on was due to hold modeand it sounds like the gates are working OK when you are in poly mode, so 
I will assume that the key assigner MCU is working correctly.
   You said that the outputs of the 4051 are -10v, so maybe your original 
idea was correct, that this chip is bad.   Please check the DAC outputat pin 1 of IC9.   It should be cycling between several different levelsif several keys are pressed.   Then check pin 3 of IC39 and also pin 3 
of IC 31 and tell us what you see.  Maybe the anti-log circuit is 
not working.
    When looking at digital signals, its important to note if the logic levels 
look OK.   The low level should be within maybe 0.5 volts of gnd.   The high levelshould be 4V or higher usually.   If you see mid-levels it's usually a problem, unlessyou are looking at a tri-state data bus, like on memory chips.   That bus will floatwhen nothing is being accessed, and can be in the middle at that time.
   Also, if the logic is 4000 series and is being operated at 12V or more, then the 
logic levels would be much higher.   But it can also be operated at 5V, like IC31 and 39,
and use std levels.

     Bob

      From: "mpe1969@tpg.com.au [PolySix]" <PolySix@yahoogroups.com>
 To: PolySix@yahoogroups.com 
 Sent: Sunday, May 3, 2015 7:40 AM
 Subject: [PolySix] Re: Key assign mode issue
   
    Hi there, I've been away for the weekend but managed to have a quick look tonight. My oscilloscope is a primitive analogue so I'm a little limited. However I had a look at the pin 9 of of ic4 and ic5. They both seem to have the same 'small  fast clock-like pattern (for want of better description). I checked gates 0-5 and all send  out a 4v (my arp switch is broken - my replacements arrived last fri so will repair this week). I push a key 6 times and on each gate I will get 4v - one in six hits.My lights do turn off on poly but not when hold is selected.
I checked power on all ic's  around this area and they are getting the 5v dc (pin 16).Other points noted:Nothing on outputs from ic2 (will recheck this in the next few days)ic 131 5vc on pin16, but -10dc appears on most of c131's outputs (constant)I checked some outputs on the main cpu, most that I tested showed a square wave looking shape. 
Once again, I will redo these checks next week. (and gather some more accurate info) I just got home and thought I would have a quick look.Thanks once again.