Problem with monitor and electromagnetic interference

[medgirl]

I recently got a new computer (Dell 8400) with a 256 MB nVidia GeForce 6800
video card. The monitor is the Dell M993s 19" CRT. I found that I could
not use any refresh rate above 60 Hz. If I set it higher, I had an
unacceptable amount of wobbling in the picture. After trying several things
(different monitors, different resolutions and color depths, new video card
drivers), I finally
moved the monitor, computer, mouse, keyboard, and surge protector to
another room, where everything worked perfectly. I also tried hooking the
computer up with an extension cord to the same plug we had been using before
and, again, everything worked perfectly at all refresh rates. Incidentally,
the image is much nicer at refresh rates of about 75 Hz or higher. I can
definitely tell a difference in comparison to the 60 Hz, though, honestly, I
can't distinguish much difference at >75 Hz. I really would like to be able
use at least a 75 Hz refresh rate. Any suggestions as to how to fix this
problem? I have tried removing various peripheral devices one by one, to no
avail. I also tried a ferrous choke device on the monitor cable, which
worked for a friend of mine, but it did nothing. Moving the whole setup
might solve the problem, but I really don't have another place which would
be great to place the computer. If it's related to the setup of the system
itself (peripherals and so worth), that won't help anyway. Is there any way
to shield the monitor which is inexpensive? Any other suggestions?

Thanks,
m

 

[Mxsmanic]

Incidentally, the image is much nicer at refresh rates of about
75 Hz or higher.

In what way? You're configured to run non-interlaced, right?

I can
definitely tell a difference in comparison to the 60 Hz, though, honestly, I
can't distinguish much difference at >75 Hz. I really would like to be able
use at least a 75 Hz refresh rate. Any suggestions as to how to fix this
problem?

If it definitely wobbles in certain physical locations, your only choice
is to move the monitor or find the source of the interference and
eliminate it. You could try shielding the monitor, but that could get
expensive and awkward.

Odd that it happens only at higher refresh rates; on the rare occasions
when I've seen this, it seemed to occur at any refresh rate. Maybe
someone else can explain why.

 

[medgirl]

In what way? You're configured to run non-interlaced, right?

There's less glare at 75 Hz. Above that, I can't discern any difference.

If it definitely wobbles in certain physical locations, your only choice
is to move the monitor or find the source of the interference and
eliminate it. You could try shielding the monitor, but that could get
expensive and awkward.

Odd that it happens only at higher refresh rates; on the rare occasions
when I've seen this, it seemed to occur at any refresh rate. Maybe
someone else can explain why.

Actually I've been doing a lot of reading about this. It seems that
electrical stuff tends to run at 60 Hz and so in some way doesn't distort
the monitor when it's at the same refresh rate (though there can be
different problems at 60 Hz), but when the monitor is running at a different
setting, there is distortion.

 

[Gary L.]

Interlaced modes for PC monitors haven't been used in over a decade.

There's less glare at 75 Hz. Above that, I can't discern any difference.

It looks better because there is less flicker. A refresh rate of 60 Hz
bothers most people, 75 Hz is good for some. I need a CRT at least 85
Hz or else I get headaches.

Actually I've been doing a lot of reading about this. It seems that
electrical stuff tends to run at 60 Hz and so in some way doesn't distort
the monitor when it's at the same refresh rate (though there can be
different problems at 60 Hz), but when the monitor is running at a different
setting, there is distortion.

This is usually (but not always) due to interference with the building
electrical wiring. You demonstrated that this is the case by moving
the computer to another room and eliminated the problem. Sometimes
moving the computer and/or monitor just a few inches or changing the
spatial orientation (i.e., rotating it 90 degrees) will lessen or
eliminate the problem. Shielding is usually not very effective.
Different equipment may be less susceptible, and flat panel LCD
monitors are generally immune from this type of interference.
- -
Gary L.
Reply to the newsgroup only

 

[medgirl]

Interlaced modes for PC monitors haven't been used in over a decade.

I think you're getting some quoting mixed up - I'm not the one who mentioned
interlaced modes.

This is usually (but not always) due to interference with the building
electrical wiring. You demonstrated that this is the case by moving
the computer to another room and eliminated the problem. Sometimes
moving the computer and/or monitor just a few inches or changing the
spatial orientation (i.e., rotating it 90 degrees) will lessen or
eliminate the problem.

Unfortunately, moving the computer or monitor slightly or to the end of the
desk, etc. has no effect. I think I'm either going to have to move it to an
entirely new spot or give in and get an LCD.

m

 

[J. Clarke]

I think you're getting some quoting mixed up - I'm not the one who
mentioned interlaced modes.


Unfortunately, moving the computer or monitor slightly or to the end of
the
desk, etc. has no effect. I think I'm either going to have to move it to
an entirely new spot or give in and get an LCD.

If the problem is noise picked up by the signal cable then an LCD won't
help.

Check very carefully the routing of the monitor signal cable. Is it passing
near the base of a high-intensity lamp (the little "Tensor" lamps that were
popular a while back for example) or any kind of fluorescent lamp? How
about a wall-wart transformer? Anything else that _might_ be generating an
oscillating magnetic field? That's the most common cause of the kind of
problem you describe. Even if you're sure it's not, check--there may be
something there that you didn't notice without being primed to look for it.

 

[Gary L.]

I think you're getting some quoting mixed up - I'm not the one who mentioned
interlaced modes.

I understand that it was "Mxsmanic" that made this comment and not
you. I just wanted to eliminate this red herring.

Unfortunately, moving the computer or monitor slightly or to the end of the
desk, etc. has no effect. I think I'm either going to have to move it to an
entirely new spot or give in and get an LCD.

I did have one system where a defective video card caused this
symptom, but if your system works correctly in another room then EM
interference is the likely culprit. If you do decide to go with a new
monitor, be sure you can return it on the outside chance that the
problem is something in the computer and not the monitor.
- -
Gary L.
Reply to the newsgroup only

 

[Mxsmanic]

Interlaced modes for PC monitors haven't been used in over a decade.

I still see people running interlaced. Usually some problem at
installation has left them with a default video setting designed to run
on anything, and often that means an interlaced video mode with low
resolution and a low refresh rate.

 

[Mxsmanic]

I understand that it was "Mxsmanic" that made this comment and not
you. I just wanted to eliminate this red herring.

It's not a red herring; it's a real problem that I've occasionally had
to fix. A lot of people won't notice that a monitor is running
interlaced unless they are told, but they will have the subjective
impression that the image isn't as clear.

 

[Not Gimpy Anymore]

I think you're getting some quoting mixed up - I'm not the one who mentioned
interlaced modes.


Unfortunately, moving the computer or monitor slightly or to the end of the
desk, etc. has no effect. I think I'm either going to have to move it to an
entirely new spot or give in and get an LCD.

m

You might try to determine the cause of the field - for example, desktop
fluorescent lamps are notorious for emitting magnetic fields, and can cause
the kind of interference you mention. Look for nearby motors as well, even
on the other side of the wall may cause issues. A nearby TV set could well
be the culprit, or even placing two PC monitors (CRT type, that is) too
close
to each other will cause interaction. Try turning various appliances off &
on to see if there is any effect, and narrow down the possible culprit.

Magnetic field radiators within a home are generally not hard to identify
and move or remove - it's highly unlikely you are seeing any effect from a
radiator beyond your area of influence.

HTH,
NGA

 

[J. Clarke]

You might try to determine the cause of the field - for example,
desktop
fluorescent lamps are notorious for emitting magnetic fields, and can
cause the kind of interference you mention. Look for nearby motors as
well, even on the other side of the wall may cause issues. A nearby TV set
could well be the culprit, or even placing two PC monitors (CRT type, that
is) too close
to each other will cause interaction. Try turning various appliances off &
on to see if there is any effect, and narrow down the possible culprit.

Magnetic field radiators within a home are generally not hard to
identify
and move or remove - it's highly unlikely you are seeing any effect from a
radiator beyond your area of influence.

Also, look for the _cable_ to be passing close to the source of the field.