> > This seems to be because I measure a steady 0.6V on pin 6 of the transformer > (p4, PSU Sheet 3). I just can't imagine where it might be coming from as the > chopper won't be running. I had previously removed the transformer and there > are no shorts between the pin 5-pin 6 winding and any of the other pins on > the transformer. I checked all the DC outputs of the PSU when powering the > 7812 from the bench, both on a working PSU and the non-working one. They are > all at zero except the -12V output on the non-working PSU, which is +0.6V. > But the voltage can't come out of nowhere. >
I've looked at it some more. On page 5 (control module sheet 1), at the non-inverting input of E1b, there is a 75k resistor and 16k9 I think? resistor between -12V and V2 which is derived from Vstart. Perhaps this would account for the +0.6V? (Ignore what I said earlier about the possibility of one of the two diodes connected to pin 6 of the transformer being shorted. The 51 Ohm (or is it a 5 Ohm?) resistor across one of them would look like a short compared to 75k.) Regards, Peter Coghlan.
