Shaky monitor

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I've got what I think may be a really tricky issue.

In a medical environment we have terminals set up using WYSE 3125SE
thin clients with Dell 15" Flat Panels. Some of the terminals are
getting shaky monitors (the image literally shakes left and right). We
have found that replacing the monitor cable or monitor will solve the
problem temporarily but the issue returns, though no specific
time-frame on how quickly it returns (sometime within a few weeks). If
we plug a monitor that is shaking into another input (a WYSE box that
is not shaking or a laptop) the shakyness goes away. If we take the
entire setup (WYSE box and monitor) offsite it goes away. The one time
I have been able to get the shaking to start happening while I was
there was to put a "good" monitor on a "bad" WYSE box (no shaking) and
hold the monitor cord up to a x-ray viewing box and the screen began to
shake a small amount.

I have the beginnings of a theory, but there are some holes. Anyone
else have anything? Questions, suggestions to try?

Re: Shaky monitor

What are machines plugged into, are they filtered through ups? My monitor
shakes to a 1970's washing machine my upstairs elderly neighbors run, really
badly without ups. Ups slowed this shaking to a minimal.(we aren't even on
the same fuse box!) Your getting a wave matching the monitor freq. in other
words. Filter it somehow.

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Re: Shaky monitor

Currently machines are plugged directly into the wall. We had one
station plugged into a UPS for about an hour, but did not see a
noticable difference during that period.

Should it be left in longer? Might this prevent the problem from
occuring if we set up a clean (not shaking) terminal on a UPS?

Re: Shaky monitor

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The fact that replacing the monitor cables temporarily fixes the problem
sounds much like you are experiencing a shielding or inductive feed over
from another device.

A couple of things that might be worth trying.

1) See if you can change the screen refresh rate on the base unit to another
value, usually a higher one.

2) Try looping the monitor cable and or power cord(s) a couple of times
through an iron powder toroidal core.  I have had luck doing this but
sometimes it takes one at both ends of the monitor cable.  I'd try with just
the monitor cable first and then add them to the power cords if needed.

3) Like bgd mentioned, a UPS might filter out the interference but it may be
cheaper to use something like a TripLite line conditioner if battery backup
is not needed.

4) Low tech but try wrapping the monitor cable with aluminum foil, as
shielding.  I have seen decorative colored foil in gift wrapping departments
if the plain aluminum color clashes (grin).

Re: Shaky monitor wrote:
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Which monitor cord, the video cord or the AC cord?  Is the video analog
or digital?

I'd first try different scan rates for the video outputs, including 60
Hz.  If that doesn't help, see if the interference is coming from the
AC powe lines by try other AC outlets, preferrably some located far,
far away (don't rule out using a 50' extension cord for this), or,
better yet, an UPS unplugged from the AC power,  To check for a ground
loop problem, temporarily plug the monitor in a 3-prong to 2-prong
adapter with its ground connection bent back so it doesn't contact the
ground screw.

If the shaking is abrupt, it's probably from a high frequency source,
such as digital equipment or horizontal sync pulses from another
monitor, especially the CRT type, but if it's at a smooth and even rate
its more likely low frequency, such as from a ground loop, motor,
transformer, or fluorescent lamp ballast.

Covering the monitor with foil may help, but don't block the
ventilation holes.  Grounding the foil to the shield of the video
connector may make it work better.

It's possible the Dell monitors are just badly designed, with sync or
sweep sections that aren't very tolerant of interference.

Can you ask one of your biomedical equipment technicans while they're

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