from N0IJ
Last summer, the power supply for my 486DX66 quit and was replaced by the
waranty provider. Being that it was summer, very little operating was going
on so no problems were detected--the computer worked fine.
This fall, I finally realized that I was getting lots of noise from the
computer and started looking! The "hash" was real bad on 40 & 80 only--only
slightly noticed on 160--typically about S3-5 on 40/80. It became real
significant when I blew the SS phone weekend by not staying on 40 long enough
because of that noise! I also fully realized the significance on 80 while
chasing VK0IR. Heard the eastcoast pile, but only occasional dits from
VK0IR. Checked out of the log program and turned off the computer.
Amazing!! Ambiant "noise" went from S2 to zero and they jumped right out of
the noise! Possibly the most exciting QSO of my life followed!
Now to the chase! Re thought a few posts from W0UN back a couple months and
did lots of the obvious stuff--toroids on AC lead, ferrite beads on other
connections, played with tin foil around vents, etc. NOTHING IMPROVED!
Moved the full tower case up on the op table and started removing
things--bingo, when I pulled the VGA line, about 1/3 of the noise went away.
Brought home my other 15" monitor from my office and swapped them out. The
office one was totally silent. It said on the front--"low radiation"! Guess
it was. My old one--also a 15" CTX now resides at the office. Removing
everything else made no difference. Now, I suspected that the power supply
was the main culprit! Ordered a new PS from an outfit in Mpls after talking
to one of their techs. Cost about $60 for a 250 watt which is probably 2-3
time the price of the other one, but it was UL approved and they considered
it one of their "better" ones?? Anyway, it completely cured the noise, and
the amazing thing is that I tested it with the box still on the operating
desk and the computer cabinet off! I can't believe how quiet the bands
sound! Moral of the story, check the monitor by just pulling the VGA plug,
and then consider the power supply. The only real physical difference in the
two power supplies detectible by looking at the sealed case except for a lot
more logos, seals, certifications, etc., is the good one has 4 wires to the
power switch and a seperate green wire ground. The bad one has only 2 wires
and no ground??
Sorry, for BW, but I think this could help a lot of folks.
John N0IJ
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