@rastro
Thank you very much for the Feedback and your kind words.
Pin4 Gain, I uploaded the block schema for the NE5561 and as far as I understand it Pin4 Gain is the output of an OP-Amp which is feedback using R12 to the negative input of it Pin 3 (Fb) therefore I assumed it would affect the gain?!
Concerning the +55V I was wondering why they need it to begin with, the voltage where the regulation of the NE5561 is based on comes from the +5V side (A8,B8,C2,D2,A4,B4) and Vcc should be provided by R7 and D13 12V zener diode so why bring it back from the +55V side?
I upload a screen cap from my scope showing the duty cycle on R11 and the over current voltage on R19, besides the spikes at the beginning of the cycle I would expect somehow a steady increase of the voltage until it hits the 0.5V trigger for current protection which shuts off the duty cycle on pin7, not the spikes as seen on the scope capture.
Now the voltage on R19 drops but the duty cycle is not kicking in again, which it should based on the datasheet of the NE5561.
When I look at the scope picture I assume that the “fuzzyness” of the duty cycle shortly prior to shutting of complete is the due to the fact that the over current protection is already kick in and the subsequent drop of voltage on R19 under the 0.5V threshold immediately activates the cycle again.
Why the duty cycle stops completely for the remainder until it repeats this behavior is beyond me. Having said that I also monitored the Voltage on Pin 3 (Feedback) which stays at ~5V for the whole time which would be correct as far as the regulation goes.
Yes I replaced D7 with a new 12V Zener Diode and I could measure 12V on pin4 of the transducer.
I was working on the CPU board to fix the noise issues for VCO2 when I noticed the solder blob on the connector back to the power supply. I grabbed my desoldering Station to clean it up. The whole PCB was on angle where I couldn't see that by desoldering the solder blob I accidentatly created a short between the two line and when I powered it back on it didn't boot and just one LED lit up