|Actual Voltages -Circuit|
I measured the S.O.T base voltage and it was 0.02 volts. I followed the start up circuit divider and the voltage was ok and no resistor was open.
But from the above voltage measurement you find the Zero volts at the base of the s.o.t is suspect.
Either the S.O.T (v513)is sorted base-emitter because its taking the voltage to the ground. Or V512(c3807) is shorted collector-emitter because it’s also taking the base of the s.o.t to the ground. Or capacitor c517 across the collector emitter of v512(c3807).
I removed the two transistors i.e. s.o.t(v513) and driver v512 and measured them out of circuit together with cap c517.
To my surprise the S.O.T v513 (C4429) was shorted Base-Emitter junction i.e. was 82 ohm both ways on diode test on my Dmm meter. It should have been high and low ( I mean the B-E junction has two reading meaning the transistor is shorted B-E junction which is very rare.
If there is zero voltage at the output then most probably the primary section is the cause of the problem.
Narrow down your faulty circuit (area) by use of voltage testing only. This one is a very fast and valuable method I have come to learn.
Let meet in the next class