Help to repair oscilloscope Philips PM3207 (Algemeen)

door Maurice , Dordrecht, 06-11-2020, 01:25 (1270 dagen geleden) @ edison

I am also worry about that oscillating BC337.

Could indeed something with that transformer.
Pull secondary R811 and series with a 10M Ohm resistor to ground.

Now you have only made a rough power supply.
Again at R808 that 30kHz as Onno mentioned.

See what happens.
Remember that with BC337 you short out -12V to +12V
Only to the fact of delay of current in the coil T801 it will act as a resistor.
But if that delay is a bit too long it will act as a DC and there BC337 will blow.
As if any other big transistor at this point.

So don't lower the frequency, keep light bulb in series too.

That is the main problem with PWM supply's.
If there is even a minor problem like chain reaction all components give up.

Than what you can do is measure that transformer with frequency.
Think just solder out.
Put primair winding frequency and parallel your scope.
Find a voltage peak at 1 high frequency.

Then look up internet how to measure that coil impedance through scope and generator.