Help to repair oscilloscope Philips PM3207 (Algemeen)

door Maurice , Dordrecht, 04-11-2020, 11:16 (1290 dagen geleden) @ Onno-I

Onno,
Indeed so.
There is lot going on in those pwm's.
Don't see why that zener instead of a diode.
Maybe to level the C802 voltage with some timing issue that is.

As I stated think at the moment there is nothing going on and just a steady
dc mode. The reason BC337 get defect.

There must be a problem with that feedback not reaching D801 pin 3.
Or though those secondary capacitors, some defect resistors.
It is essential that secondary circuit to be in good condition.

May be at start up there is a little oscillation but due to f.i. bad capacitors
it is not reaching the voltage and so raising the voltage to point of pure dc
and oscillation shuts down.

There for TS needs a scope, but hé that one broke down.
Also a lack of puls generator to manually oscillate that BC337 to see if somehow
you get a little voltage at C807.