This continues the saga of the troubled 961PS that
several reflectorites originally helped me diagnose a
couple of weeks back. I replaced the rectifier board
in the 961PS that's been giving me trouble, because I
knew the bridge had a blown diode. Ten-Tec no longer
stocks the old bridge but sold me the entire rectifier
board at a very reasonable price.
The bridge pins on the board I received are a
different configuration so I went by the component
labelling, only to find out later that the + and -
terminals were mislabeled in reverse. After blowing
the mains fuse, it didn't take too long to figure this
out and switch the wiring.
What I'm finding now is that when I turn on the
supply, the LED comes on and the DC output looks good
for one second, and then shuts down. I would really
appreciate help troubleshooting this, although you
probably need a 961 schematic to help. I just don't
have much experience with regulator circuits, and the
961 is pretty complex.
The unregulated dc looks healthy at 23VDC. The bias
voltage at the base of the pass transistors comes on
at 14V and drops to 0 at the one second mark. The
over-current trip comparator U2B (LM358) seems to
generate a pulse at that one second mark on output pin
7. Pin 6 is at 20volts and pin 5 starts out at 8volts
and drops to 0 at the one second mark. I don't know
if the Trip Adjust in these supplies ever needs
adjustment?
I am equipped with an oscilloscope if anyone can
suggest points to check. Or is it simply a case that
a component was damaged when the rectifier was reverse
wired?
If anyone can lend some help here, I'd really
appreciate it. Love to get this baby up and running
again.
Thanks for the long read & very fb 2K to all,
Barry N1EU
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