Different boot problem...

DoN Nichols dnichols at ceilidh.beartrack.com
Sat Mar 2 12:27:07 AEST 1991

In article <12877 at helios.TAMU.EDU> n138ct at tamuts.tamu.edu (Brent Burton) writes:
>Well, another update to the adventure.

	[ ... ]

>We tried 2 other times with failure.  Then, we decided to check the power
>supply voltages and the machine booted (this is insane).  Two other
>attempts at rebooting worked fine and it's running right now!!!
>The power supply is providing the following:
>spec'd voltage        actual
>-------------         ------
>   +5.0V               4.97
>   +12.0V             11.95
>   -12.0V            -12.00      (taken with new digital meter)
>Where should these values lie and when I need to adjust them, which
>pots on the ps board do I mess with?  (so many pots, so little patience)

	Only the +5V and +12V are adjustable.  Probably you should aim to be
a "lettle grey cells" (oops, a little high - watching too much Poirot :-).
Probably +5.1 and +12.2.  The pots ARE labeled, but the labels tend to be
hard to see from any reasonable angle of view.  Looking at a 3B1 power
supply, +12V is near the center of the multi-pin output power connector, and
+5V (R-108) is near the inboard end of the same connector, with its label under a
yellow and a black wire, and the curve of U1 (whatever that is - maybe an
opto-isolator :-).

	If you ever HAVE to adjust the -12V, do it by replacing U101 (the
regulator chip).

	Good Luck
Donald Nichols (DoN.)		| Voice (Days):	(703) 664-1585
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