Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!comix!jeffl
From: jeffl@comix.UUCP (Jeff Liebermann)
Newsgroups: comp.unix.i386
Subject: Re: < 3 SCSI Drives on ISC 2.02 (problem) >
Summary: Cheap power supplies
Message-ID: <66@comix.UUCP>
Date: 5 Aug 90 02:57:27 GMT
References: <675@unlisys.UUCP> <3491@tmiuv0.uucp> <11119@alice.UUCP>
Distribution: comp
Organization: COmmittee to Maintain Independent Xenix
Lines: 31

In article <11119@alice.UUCP>, debra@alice.UUCP (Paul De Bra) writes:
> In article <1990Jul28.011957.301@scuzzy.mbx.sub.org> src@scuzzy.mbx.sub.org (Heiko Blume) writes:
> >rick@tmiuv0.uucp writes:
> Yep, power supply smoking can be very unrelated to power consumption.
> The power supply in my Everex Step 386/25 smoked after less than 6 months,
> with only 1 drive and 4meg in the system. I put in another one, a 230 Watt
> thing from a local store, and it smoked a couple of months later, shortly

I do component level repair on some hardware including power supplies.
About half of the power supplies I've seen have a problem with poor
solder connections on the *SINGLE* *SIDED* circuit boards.  What
happens is the vibrations (at 40Khz or so) from the transformer(s)
mechanically couple thru the leads and fracture the solder connections.
These physically large components also absorb considerable heat
during wave soldering that tends to cause cold (crummy) solder connections.
I can usually spot an annular ring around the pins.  Re-soldering
with a big iron solves the problem.

Another common disgrace is that the switching transistor(s) and
diodes are spring clipped instead of screwed to the heat sink(s).
Clips do not guaranttee sufficient heat transfer and will result
in elevated device temperatures, and early failures.  Semiconductor
failure due to inadequate heat sinking accounts for another 30%
of the repairs.  The rest are mechanical damager, filth, paper
clips, staples, screws, fan failure, and such.

-- 
# Jeff Liebermann   Box 272   1540 Jackson Ave   Ben Lomond  CA  95005
# (408)336-2558 voice  (408)429-0483 digital pager      CIS:73557,2074 
# PC REPAIR & RF DESIGN.   uunet!comix!jeffl   pyramid!vdx!comix!jeffl
# universe!milky_way!solar_system!earth!na!us!uunet!comix!jeffl