If I could add to my diatribe :
Usually, in the smps section, defective or faulty caps will become resistive (from a few ohms ot a few Kohms).
These caps are .1UF at 25V, surface mount and in the 15V control circuit; They should measure a large resistor value, > than 1M (or close to!).
C201 (other side of the junction of R375) should measure greater than 60K ohms. If C201 should measure lower, remove the cap and measure its DC resistance.
C196 (220UF 35V) is the kick start cap. Its function is to offer a bootstrap kick voltage to start the smps process. While the smps has not started, the cap will fill up and empty at approx .5 to 1 Hz. (the oscillation you've been observing).
Also, you will notice some 48K resistors. (By the way, are the 48K resistors big, fat and blue? If the resistors are big, fat and blue, they will all need to be replaced!)
D28 and 29 are 15V zener diodes. You should be able to measure the 15V on both diodes (total: 30V); Some of the 48K resistors are used to drop the voltage from 170V to 30V (340V when smps has started).
Note: You mention some voltages at the IGBT. If reference of your meter is on the emitter of either IGBT, I believe you should not have more than 15V at the gate with a signal of perhaps 5 volts or so. I'll get back to you if it is wrong.
joustMember Since 02 Dec 2004
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