Help to repair oscilloscope Philips PM3207 (Algemeen)

door Onno-I , 06-11-2020, 08:26 (1479 dagen geleden) @ edison
Gewijzigd door Onno-I, 06-11-2020, 08:42

Two questions:
1- what were the waveforms on the base, collector of V801 and on the primary side of the transformer (where it was connected to the bulb)

2- did you have spare BY409's to replace V802, 803? (I wouldn't have the originals, but use BY176 from an old TV)
they are quite special rectifiers, rated at 11,5kV. In 1980-1990 color TV's there would have been one (or an equivalent) for the focusing voltage to the CRT.
They are quite unlikely to fail in this place, where they get a peak inverse voltage of 1500V (3000 if you take a wide margin)

I wouldn't replace them by an ordinary 1N4007, maybe a chain of four each if I was out of options.

By the way, it you test a BY409, they have a forward voltage of 36V so you might think they are interrupted if you test them using the diode test function of your DVM.