Hi Ludwig.? Thank you for the analysis.? To answer your first 3 questions:
The GND lead was clipped to the bnc output connector
The ground lead is approx 150mm
The original BS170's are in circuit.
Unfortunately while looking for the waveforms you asked for, I must have shorted the +ve at the BS170's as they have no Drain voltage so I think Q507 has been destroyed as there is 11.5V on its Source, nearly 11.5V on its Gate and 0V on its Drain.? So at this stage I have ordered a replacement AOD403 from Digikey and it will probably take a week or so to be delivered.
Thank you for your help to date and I will update when I have replaced the AOD403.
Regards
Greg
