other electrical appliances interfering w compute rmonitor - how to troubleshoot

[Dave Botsch]

So, I have an LCD tv hooked up to a Scientific Atlanta cable box on one
outlet. On the same circuit (but different outlet), I have a CRT computer
monitor plugged into an APC Backoffice UPS (into which the computer is
also pluged in). On a different circuit in the kitchen are items such as
the microwave and toaster oven and the fridge.

So, if I run the microwave, the picture on my computer CRT is quite shaky
and I get quite a bit of audio hum in the sound from the cable box/lcd tv.
If the toaster over is running, the crt is less shaky, and I don't notice
any audio hum. If the fridge is running, there is a tad of shakiness
(could be mistaken for poor refresh rate on the crt). It's unclear if the
water heater is causing any problems, and the window AC does not seem to
be causing noticable problems, either (tho, it's upstairs on a different
circuit). However, I have actually seen the shakeys seem to get better
sometimes when the toaster over is on and then the window ac comes on. The
washing machine and dryer are definitely causing some monitor shakeys.

So, any thoughts on what is going on and what I can do to eliminate the
interference problems? I'm guessing not a short to ground since no circuit
breakers are blowing. Is there some sort of grounding loop? Some sort of
inductance going on? Something I can test for with a multimeter and then
go to the apartment people and say "look, this needs to be fixed, here's
the evidence"?

Thanks in advance!

ps this was posted in a different group and the folk there suggested this
group.

 

[isw]

So, I have an LCD tv hooked up to a Scientific Atlanta cable box on one
outlet. On the same circuit (but different outlet), I have a CRT computer
monitor plugged into an APC Backoffice UPS (into which the computer is
also pluged in). On a different circuit in the kitchen are items such as
the microwave and toaster oven and the fridge.

So, if I run the microwave, the picture on my computer CRT is quite shaky
and I get quite a bit of audio hum in the sound from the cable box/lcd tv.
If the toaster over is running, the crt is less shaky, and I don't notice
any audio hum. If the fridge is running, there is a tad of shakiness
(could be mistaken for poor refresh rate on the crt). It's unclear if the
water heater is causing any problems, and the window AC does not seem to
be causing noticable problems, either (tho, it's upstairs on a different
circuit). However, I have actually seen the shakeys seem to get better
sometimes when the toaster over is on and then the window ac comes on. The
washing machine and dryer are definitely causing some monitor shakeys.

So, any thoughts on what is going on and what I can do to eliminate the
interference problems?

Sounds like magnetic interference. Try moving the CRT at least 10 feet
away from every other unit and see what happens. If that eliminates the
problem, then one by one see just how close the units can be without
causing problems -- magnetic fields fall off very quickly with distance;
much faster than distance^2.

I have a small floor fan that gives my CRT the shakes at nearly four
feet, but presents no problem at about six.

Isaac

 

[Dave Botsch]

It is at least 10 feet away.

Funny thing is, I'd swear this problem did not exist when I first moved
in, and cannot recall it happening prior to the summer. The LCD tv is even
further away.