From: Joe Desbonnet (joe at domain local.ie)
Date: Thu 02 Sep 1999 - 02:17:58 IST
Actully mains here has a lower frequency than in the US (50Hz here, 60Hz in
US) . And if your monitor didn't like the higer voltage it's smoke you
would see -- not a jitter.
As far as I know monitors convert the AC into DC immediatly (some low
voltage, some very high voltage) so the frequency of the mains should not
I've seen this sort of problem before when there is a AC line carrying high
current running very near your monitor (ie within a meter or two). Or when
some electro-mechanical device is running near by (eg fan).
One way to narrow the possible causes of your problem is to temporarly move
your computer to another room (or another house) and see if the problem
persists. Or try borrow another monitor and see if problem is the same with
I don't think Al foil will solve your problem as its *magnetic* interference
that causes the jitter. Al will not shield against that. You need mu metal,
or a big iron box.
Having said all that, I've seen cases of monitor jitter that were
un-explainable and unsolvable and I simply filed as yet another computer
On Thu, Sep 02, 1999 at 01:50:41AM -0400, Peter Heslin wrote:
> Apologies if this, a hardware question, is too off-topic, but I did not
> know where else to ask. I have just moved back to Dublin after living in
> the USA, bringing back with me a fairly cheap 17" monitor, bought over there.
> When I started to use it here, the image was jittery, and so at first I
> thought it had got a knock in transit, but the problem has been stable and
> intermittent since then, so I have been thinking of other causes. I thought
> it might be that the monitor did not like the higher AC voltage and frequency
> here, even though it is rated to tolerate it. Turning off nearby appliances
> sometimes helps, but this is not curative.
> I then did a search on the web and discovered that many people in the
> vicinity of electrical power lines experience magnetic jitter similar to my
> symptom. As it happens, I positioned my desk next to a window that is about
> 30 m. away from the overhead power line for the DART train here in Dublin.
> And when I use my laptop on my desk here, every time the computer is active,
> the radio on my desk gets a burst of interference, sending static for
> each keystroke. I've had the laptop a long time in Ireland and never
> saw anything like this before. So I am guessing that the power lines set up a
> magnetic field which the CRT can normally cope with, until some other
> appliance sets off a perturbation in that field, which is then propagated to
> the monitor (and radio, etc.).
> Before trying to fix this, I thought I should find out if anyone else has had
> the same problem. My potential solutions include:
> 1) Try to ignore it while I slowly go blind.
> 2) Move the desk to the other side of the room (unlikely -- involves effort).
> 3) Cover the monitor in aluminum foil (the wife won't be happy ... )
> 3) Buy a video card with a faster dot clock than my current 2 Meg S3. It
> can't drive 1024x768 at domain 85 Hz, or so it seems, but the monitor says it
> can. The problem seems to be much diminished at 800x600 at domain 85Hz, but I
> haven't tested this extensively; I'd rather go blind at 1024x768 at domain 75 Hz
> with jitter.
> But before expending money or effort, I thought I'd see if this is a
> familiar problem among savvy Dubliners.
> Peter (list newbie)
> Irish Linux Users' Group: ilug at domain linux.ie
> http://www.linux.ie/mailman/listinfo/ilug for (un)subscription information.
> List maintainer: listmaster at domain linux.ie
This archive was generated by hypermail 2.1.6 : Thu 06 Feb 2003 - 13:04:31 GMT