Discussion about the Korg PolySix synthesizer

3.5V on D2 is perfectly OK, there is a 10K resistor is series and the
voltage is only 5V. This leaves less than 1mA so the Zener voltage is
not even reached. Furthermore you cannot check it with the DVM; most
DVMs can measure up to 2V in the diode check range.

Did you ever make the following test (MANUAL mod, all knobs fully CCW):
turn up a single knob to max and measure the corresponding 4051 demux
output.
For your reference and clarification here is a list which knob drives
which 4051 pin (on KLM-367):

      knob         IC    pin

   Effects Speed   18     13
   VCF Cutoff      18     14
   VCF EG Int      18     15
   VCF Resonance   18     12
   EG Attack       18     1
   EG Decay        18     5
   EG Sustain      18     2
   EG Release      18     4
   VCF KBD Track   19     13
   PW / PWM Depth  19     14
   PWM Speed       19     15
   MG Speed        19     12
   MG Delay        19     1
   MG Level        19     5

Each output should swing from -5V to +5V over the range of the knob.
Important for getting information about the root cause of the fault is
that you measure *each* of the pins when turning the knobs. In this way
you can easily detect if and which knobs are tied together (assuming
e.g. that one address line is stuck).

Next thing is to check for continuity of the P20, P21, P22, INH1, INH2,
and the DATA lines from their generation (P20-P22, INH1: CPU IC22,
INH2: IC23, DATA: R37) to KLM-370/371. CN11 is prone to failure after
battery leakage. Additionally leaked battery acid might have crawled
through the thick GND wire up to KLM-371 and damaged PCB traces and/or
IC leads there. It is important not only to check continuity but also
shorts against GND, VCC, neighbouring pins and traces.

Good luck!

Johannes


On 08.01.2014 14:52, josh.nursing@gmail.com wrote:
>
>
> Replacement Zener found and installed at D2, continuity tested around
> it, part of calibration procedure re-done, when calibrating the DAC,
> LEDs 1 & 5 are still on no matter what.
>
>
> Spent a good time reflowing and checking KLM-371 too.
>
>
> So now it feels like I am nearing a complete repair since the Polysix
> sounds really good and clean, and when I do get control over the pots,
> it's much fun.
>
>
> Somehow the signals get garbled up, so if swapping the two new 4051s
> does not help, I will also try a swap of the CPU as well as testing each
> 4051 individually on a breadboard.
>
>
> Yash
>
>
>
>