Path: utzoo!attcan!uunet!peregrine!elroy!ames!pasteur!ucbvax!DALAC.BITNET!BRIGHT
From: BRIGHT@DALAC.BITNET (BOB BRIGHT)
Newsgroups: comp.sys.atari.st
Subject: RE: Mono shakes
Message-ID: <8808020007.AA19314@ucbvax.berkeley.edu>
Date: 1 Aug 88 14:43:00 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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>When you find out why it shakes, would you post it? My mono monitor shakes
>also, and I do not have a color monitor nearby when running mono. My monitor
>also locks in on different places when I turn it on, as well as a skewed look
>in one corner.
>
>John

     When I first set up my 1040ST w/SM124 monitor in my office and
booted it, I was immediately greeted with a jittery monitor.  Moving
the system around on my desk helped somewhat, but only somewhat.
Suspecting that my monitor was faulty, I borrowed another SM124, but
to no avail.  Sometimes the jitters were worse and sometimes better,
but always present.
     Must be RFI from somewhere, right?  Sure enough, on checking I
discovered that my monitor jitters were at their worst when other
people were running small electric heaters in their offices.  Only
problem was, the nearest heater was more than 30 feet away; and when I
plugged one of the heaters into a wall socket in my office, it didn't
make much difference unless I parked the bloody thing right on top of
my monitor!
     So I checked to see if the electrical circuits feeding the other
offices were buried in the wall near my system.  Nope, no wires buried
in the walls.
     "OK," says I to myself, "then those crummy little heaters must be
kicking up some line noise that my SM124 doesn't like."  So I got the
local electricians to install an isolating transformer on the circuit
in my office.  Didn't help.
     By this point I'd pretty much resigned myself to living with the
jitters 'til the warm weather appeared and the heaters were put away
for the summer.  (Small comfort in Halifax, since it doesn't get warm
until June or so!)  Then one day on the way in to work, I found the
solution staring me right in the face: there on the wall of the
Philosophy House, right outside where my office was located, and not
three feet away from my desk, was the electrical service and power
meter for the entire department.
     Since there wasn't any easy way to move the electrical service, I
moved into a new office when one became available.  I'm happy to
report that my SM124 is now rock-solid.
     So what was happening?  My guess is that the SM124 is pretty well
shielded from RFI, but is quite sensitive to magnetic fields.  Maybe
I'm wrong about this (could someone who knows more than I about such
things please comment?), but there's no doubt that those invidious
little heater fans were generating lots of RFI, and they didn't make a
lot of difference unless they were right next to my monitor.  When the
heaters were turned on, on the other hand, they were drawing
considerably more current through the electrical service and meter,
and this would increase the surrounding magnetic field considerably.
     Well, sorry to run on so long.  When I related the gory details
of this story to another guy who was having problems with his SM124,
he checked outside his house, and sure enough, his system was set up
directly opposite the electrical service.  Maybe this info will help a
few others who have so far been frustrated in tracking down the source
of their jitters.

BBB

Bob Bright <BRIGHT@DALAC.BITNET>
Philosophy Dept.
Dalhousie University
Halifax, NS  B3H 3J5  902-424-3810