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From: thad@btr.BTR.COM (Thaddeus P. Floryan)
Newsgroups: comp.sys.3b1
Subject: Re: Different boot problem...
Keywords: 3b1 boot
Message-ID: <1973@public.BTR.COM>
Date: 1 Mar 91 11:06:36 GMT
References: <12744@helios.TAMU.EDU> <1991Mar1.045750.19952@i88.isc.com> <12877@helios.TAMU.EDU>
Distribution: comp
Organization: BTR Public Access UNIX, MtnView CA, Contact: cs@btr.com 415-966-1429
Lines: 45

In article <12877@helios.TAMU.EDU> n138ct@tamuts.tamu.edu (Brent Burton) writes:
>[...]
>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)

Your voltages are well within spec (+/- 5%).  The ranges are:

  4.75  <=   5.00  <= 5.25

  11.4  <=  12.00  <= 12.6

I prefer to run mine slightly high (5.1 and 12.2) to help offset any drops
in PC trace runs, esp. to the expansion boards.

The adjustment points (ONLY FOR +5 and +12 (the -12 is provided by a fixed,
non-adjustable IC regulator)) are silk-screened on the power supply per
"+12 ADJ." and "+5 ADJ." alongside their respective pots.

The +12 ADJ point is about 2" in from the front of the power supply and about
1" inwards from the 18-pin connector to which the ribbon cable from the
motherboard connects.

The +5 ADJ point is about 2" towards the rear from the +12 ADJ point.

Be SURE to use a plastic or non-conductive shaft screwdriver when making any
adjustments, and be VERY careful.  Counter-clockwise reduces the voltage, and
clockwise increases the voltage.

The power supply MUST be loaded-down when making adjustments, and what I
recommend is a "Y"-cable temporarily attached to the HD with one set of
wires going to the power supply and the remaining set being available for
your DVM probes.  Such "Y"-cables (with three 4-pin Molex-style connectors
at each end of the "Y") can be found at most electronics and computer stores,
swap meets, ham fests, surplus houses, etc. and "should" not cost more than
about $1.

Thad Floryan [ thad@btr.com (OR) {decwrl, mips, fernwood}!btr!thad ]