HP9915B with PSU problems - test-drb@ccmp.vtda.org

18 Mar 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
fuse blows.

...
  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?

Thanks

**vp

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).