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sick '70 power supply?

   Date: Tue, 24 Mar 1992 17:22-0700
   From: paul@PERSEPHONE.aegean-sea.dialnet.symbolics.com (Paul Cross)

   I've got a 3670 that upon power up does not turn off its fault light.  I
   noticed that the main -12v light on the back back of the machine was not
   lit, though all others were lit.  I don't know if the bulb is burnt out
   or if indeed there isn't -12v.  On checking my powertec power supply,
   model 6JA5-BBF-17, all the channels were normal except channel 3, which
   was putting out 1v instead of its labeled voltage of 12.   The
   machine was fine this morning.  I had to power it down to do a board

Sure sounds like a busted power supply to me.

   My questions.

   What is the minimum board set one could put in an OBS machine and
   have the fault light go out upon power up?

Just a guess: FEP and I/O.  But it's possible that the FEP checks for the
existence of the processor boards.

   Can I adjust the voltage of channel 3? Or, is there a fuse or breaker
   that could have tripped?  Or, do I need a replacement power supply?

There are adjustments on the power supplies, but they're not intended to
provide that much range (it would be appropriate if you were seeing 11.5).
I think you need to replace the power supply.