Vintage Synth Repair

Hi,

You're a genius.
I followed you're instructions and I found out there was no signal on pin 1 of IC25 but there was a signal on pin 1 IC29
I replaced the 072 opamp chip in between those 2 chips an now everything is back to normal.

Thank you so much for your help!

Regards,

Nicolas

--- In vintagesynthrepair@yahoogroups.com, Malte Rogacki <gacki@...> wrote:
>
> This calls for a more thorough debugging.
> 
> Set the front panel controls as follows:
> 
> - Cutoff 0
> - Resonance 0
> - EG Intensity 0 (center)
> - Key Track 0
> 
> Now check with a scope the situation at pin 3 of IC23. You should get a
> proper DC voltage of +5V. If you move the Cutoff control to max the voltage
> should change to -5V. Same should apply to the outputs of IC23.
> 
> Next we check the multiplexing of the keyboard CV. For this we monitor pin3
> of IC25. Put the synth in Unison mode and press the highest note on the
> keyboard. You should get a reading on the scope that looks like DC with a
> single periodic 0v "dip".
> The keyboard CVs for the six channels start immediately after this "dip".
> You can check if they correspond to the keys pressed.
> 
> Now we set Key Track to Full, Cutoff to zero, again use Unison mode and
> press the highest key. Check at pin3 of IC23. You should basically get a
> "mirrored" reading from the one at IC25 - a weak DC signal with a single 5V
> "peak". Again the channels would start immediately after this peak. Check
> if the signals there make sense. By playing different notes you can check
> if the voltages on the input (pin 3) correspond to the voltages on the
> output of IC23 or if - for example - the voltage for channel 1 shows up on
> the wrong output pin.
>