1. Home
  2. Electronics Repair
  3. electrical wiring under load interfering w. monitor?

electrical wiring under load interfering w. monitor?

I posted on this a while back. When the fridge, water heater, washer/dryer, microwave, or toaster oven is on, my computer monitor has noticable shakies. When these things are off, the picture does not shake.

I've tried unplugging the UPS (which powers the monitor and computer) from the wall then running one of the appliances again. Same shakes, same intensity.

I did bring down a second monitor and it did not have these problems. It then occurred to me that the second monitor was sitting down on the floor away from the wall. While an appliance was on, I picked up the monitor, and moved it about 6 - 8 inches forward. The shakes decreased (note that this actually moved the monitor 6 - 8 inches closer to the actual appliance which was running).

So, what does this mean? Interference from unbalanced wiring which only shows up when something is pulling some amps?

Since I'd swear the monitor did not do this when I first moved in (but I could be wrong), is there circuitry in the monitor which is supposed to compensate for this sort of interference (circuitry which could have gone bad)?

Thanks!

--
********************************
David William Botsch
dwb7@cornell.edu
********************************
Reply to
Dave Botsch
Loading thread data ...

Hi, have seen this at a former work place. Monitors got the shakes when the lights were turned on.

All that was required was to increase the refresh rate of the video out. From 60Hz to 75 should do it.

Russell

Reply to
Russ_Verdon 

--
********************************
David William Botsch
dwb7@cornell.edu
********************************
Reply to
Dave Botsch

It sure sounds like the return path of the appliance drawing current is not in the same cable as the souorce current. That sounds like a major wiring problem. There is a magnetic field set up by the "coil" of current flow and that interacts with the magnetic deflection of the CRT beam causing the shaking. If the monitor is truly totally disconnected from the AC power mains of the house, then the only thing that I know of in 40+years of EMC detective work that would cause the monitor to get the shakes is a magnetic field, and that must be caused by current flow in a loop of wire. Normally, the out and back current flow is in conductors within a 1/8 inch spacing of each other in the same conduit or Romex wire, the currents are equal and there is vitually no discernible external magnetic field.

This sort of problem is what makes many EMC engineers drool. If the problem is consistent, you sound like you know enough to track it down. Good Luck!!

H. R. (Bob) Hofmann

Reply to
hrhofmann

How major of a wiring problem? Other than the magnetic field being generated, is it somehow dangerous? Is there anything else about the wiring that could generate such a field?

Unless it's a fire hazard, I doubt I'll be able to get the complex to actually do anything about it.

Thanks!

--
********************************
David William Botsch
dwb7@cornell.edu
********************************
Reply to
Dave Botsch

Is the building old? Do you know whether it uses knob and tube wiring which separates the conductors by several inches?

Dave Botsch wrote:

Reply to
Bennett Price

Hi!

Sounds like you've got a neutral connection that's about to fail or has failed already.

The neutral burned in two on the power pole outside my home. When it did, all of my computer monitors exhibited a shaking picture, no matter what scan rate or resolution was chosen.

Look into this, or call someone to take a look at it. Left unchecked, it could damage electrical equipment or even start a fire.

William

Reply to
William R. Walsh

I do not know. It is an old building that was just remodeled (I don't know if they ran new wiring).

--
********************************
David William Botsch
dwb7@cornell.edu
********************************
Reply to
Dave Botsch

On Mon, 07 Aug 2006 23:46:22 +0000, William R. Walsh wrote: If the neutral has failed, shouldn't there be no electricity (since there is no return path)? Or are you thinking the neutral is shorted to ground.

Is this anything I could detect w. a multimeter? Any other symptoms?

Like I said, the shaking is only when something else is on with wires that most likely run in the wall behind the monitor (for example, the AC upstairs does not affect the monitor at all, but wires prolly go up from the panel through the ceiling).

--
********************************
David William Botsch
dwb7@cornell.edu
********************************
Reply to
Dave Botsch

Hi!

There will be electrical flow. If you're in the US, power comes into your house with two 110 volt legs.

The neutral plays an important part in keeping these two "legs" of power at equal levels. Each one should normally be ~115 volts AC. I'm not sure I can explain the reason behind this, but without the neutral, you'll have voltage levels that swing wildly between the two legs.

The voltage on the more heavily loaded leg will drop, while the lightly loaded one will go up...and sometimes skyrocket up to 150 volts or so!

Yes, but the problem may have to be more severe than it is now. Set your multimeter to the AC volts scale and plug it into an outlet. If the problem is bad enough, you'll notice the voltage goes way up or way down from where it should be when other loads start or stop.

Note that momentary dips don't necessarily indicate a problem.

When someone starts a heavy load, like a vacuum cleaner or washing machine, do any (most likely incandescent) lights brighten momentarily? If they do, you've got a bad neutral connection somewhere.

That could be simple electromagnetic interference of some kind, but whenever I've seen the picture on a monitor shake in response to electrical flow, there's been an obvious culprit (like a transformer that's too close to the monitor casing) or a bad neutral connection.

Even when my digital meter showed normal voltage levels with the bad neutral, my monitors were all still shaking away...just enough to be annoying.

William

Reply to
William R. Walsh

It is also possible that the "return" for one of the 120 V circuits in question is not thru the neutral but through some other path to "ground" such as the safety ground which could be the building stelel or some circuituitous (sp?) conduit. I have seem that a number of times. The return can be quite a long distance away from the source wiring and affect a large physical area.

I would definiteoy contact the building management and say there is a serious potential safety issue. That should get their attention. if no response from them, you could consider the local building inspector if you don't mind being considered a pest. But, there is defitely something not right!

H. R.(Bob) Hofmann

Reply to
hrhofmann

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.