20 Nov
2004
20 Nov
'04
11:42 a.m.
it is? I suspect the SOC chip is an opto-isolator (it
only has 6 pins
and is curiously in a white package). Not sure about the SG chip but I
Almost certainly an optoisolator. Probably for the voltage feedback loop
(LED on the secondary side of the supply, connected to some kind of
voltage sense circuit, transistor connected to the chopper control side
of things). I think what I'd do there is connect a light
bulb in place of the
resistor (say a normal 100W mains bulb, which should be OK for testing on
light/no load), then pull the chopper transistors and power up. If the
bulb lights brightly you've probably got a short in the
rectifier/smoothing capacitor stage.
OK, with the chopper array disconnected (plus everything downstream of
it) the bulb lights very brightly when power's initially applied, then
gradually extinguishes over a period of about 5 seconds. DC output from
the rectifier is 300V. Possible dried-out smoothing cap? The bridge