HP9915B with PSU problems
vp at cs.drexel.edu
Fri Mar 18 17:02:09 CST 2005
Thanks Tony for the advice:
> Fuse still blows? Remove the diode between pin 6 of T2 and the -12V line
> and the diode between pin 4 of T2 and the V+ line (RH side of sheet 1 of
> my CPU board schematic). With those lifted, the supply is reduced to a
> simple 12V one driving no load.
I did so and the fuse held. I meassured the +12V line and it gave me
close to 12V (+11.98V). I also reconnected CR13 (the one at pin 6
of T2) and got the -12V and -5V supplies as well.
Unfortunately, when connecting the other diode (CR12, pin 4 of T2), the
> I'd supsect (a) a short in one of the output regulators _and_ (b) a
> problem with the current sense circuit (round U31, LM311).
Any ideas on how to debug this?
BTW I have another question related to another 9915 with PSU probs.
What would cause the -12V supply to produce only around -5V (i.e.
the volatages on either side of the 332 Ohm resistor are around
-5V (not equal, but close).
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