Flickering Monitors?

Anonymous Coward writes "Our SB Office runs a small 2 Server network with 4 workstations in the LAN, each connected to a dedicated APC Surge protector. The building has a backup power generator thus we didn't see the need for a UPS. For some odd reason all our monitors flicker a lot. We've tried everything from changing resolutions/refresh rates/video cards/monitors and spacing the monitors farther apart from each other - all to no avail. Could this be a building power supply problem? Some have suggested there may be some magnetic interference but visually inspecting the surroundings doesn't leave us with a culprit for the cause. Could this be fixed by the simple addition of a good UPS? Any help, tip or information would be gladly appreciated. Thank you."

Comments

Fans?

[Stigmata669]

I had this problem when I placed a table fan next to my monitor on my desk in the middle of summer. The spinning magnets cause a very annoying flicker, and maybe hopefully not do some damage. Try moving the monitors farther away from racks or the generator, and that might fix the problem.

electrical fields

[crow]

A coworker of mine who is very sensitive to screen flicker had a similar problem--every monitor he tried would cause headaches. They gave him a flat screen and that solved the problem. That was at about the time when we figured out that on the other side of the wall from his cube was a wiring closet, so it was the electrical fields from the wiring closet messing up his monitor.

If you can find the source of the problem, you might be able to shield it.

backup power generator

[President Chimp Toe]

How close is the backup power generator to your room? I think this could be the problem - due to EM inteference. A similar problem occurs if you have e.g. a large bass-box and you place the monitor next to it, which I hope you are no doing!

In fact, I have experienced exactly this where I work. There is a fscking great big generator right next door to me. My original monitor flickered like hell when I moved in to my new office. No matter what I did - where i put the monitor, whatever the settings, the flickering was completely unbearable.

The only way round the problem I have found is using a flat-screen. LCD doesnt suffer the same EM inteference problems as cathode ray. Hence no flickering.

Luckily I was able to find someone kind enough to swap monitors with, saving me some expense (my old CRT monitor was pretty darn huge and cool, though). Other than forking out for some new flat screen monitors, I dont know what to suggest!

UPS will help if it's not magnetic

[Snowfox]

A good UPS will help rectify current and voltage oscillation if it's not magnetic interference, which is the most likely cause if it's not magnetic interference.

But if you're going to lay out that kind of cash, replacing the monitors with cheap analog LCDs will make them immune to most kinds of interference and cut your power consumption significantly. Replacing them with digital LCDs (DVI-D) will make them work properly in the middle of a pile of supercharged magnets.

That said, I'd find someone who's comfortable throwing a scope on the line and checking out your power situation. If your building's UPS is throwing out an imperfect signal, it may be slowly killing your machines if left unrepaired. PCs don't take well to current variation or screwy spiked or squared voltage waveforms.

Looking with the right tool

[martyb]

I have developed a set of debugging techniques over the years that seems to work in most every situation. It's a matter of looking at a problem from the proper level of abstraction and using the tools I already know how to use:

How do you find a needle in a haystack?

1. Look for a very long time (exhaustive search).
   
2. Improve the odds; make the haystack smaller (process of elimination)
   
3. Improve the odds; make the needle bigger (adding print statements to code)
   
4. Use a magnet! (think outside the box)
   

With all seriousness, pick up a good compass at a sporting goods store and do a survey of your office. Walk around the room and see if there are any deflections. Whether it's an electric current (which induces a magnet field) or an actual magnet in near proximity to the magnet,
a good compass should point you in the right direction (pun intended!)

Things I have experienced in the past which affected my monitors, in no particular order:

• Cheap speakers placed near monitor (speakers have magnets). Ditto for headphones!!
  
• Small desk fan, even though 3 FEET away, had such a dirty magnetic field that it interfered with my monitor!
  
• Power cable from the PC and/or monitor running alongside the video cable induced flicker (60 Hz) into the video signal; when I separated the power cables from the video cables, the problem diminished greatly.
  
• Electrical cables (wires) IN THE WALL! It makes sense to set up the computer and monitor near an electrical outlet. One time, the electrical outlet into which my monitor was plugged was located directly below the back of my monitor. The power cable feeding that monitor was fed across a suspended ceiling and dropped down the wall to the outlet... immediately behind the yoke of my monitor! I moved the monitor 12 inches to the side and the problem disappeared.
  
• If the monitor's video cable is replacable, try using a video cable with a choke coil on it.
  
• Florescent lights' refresh rate (60 Hz) beating with the refresh rate of my monitor. I unscrewed the bulbs in the overhead florescent light fixtures and saw the problem go away.
  

One other thing to try is to bring the PC, monitor, and all peripherals home and see if the problem exists there, too. If so, then it's likely there's something flakey about your equipment. If they are okay, then it would indicate there's some environmental factors at your office.

Good luck! And please fill us in on what you find!

Step by step

[maggard]

Summarized:

We've got funky electrical/magnetic problems going on in our office splace - any ideas?

1. Funky power is going to shorten the life of your hardware significantly. I used to work at a company where a series of IS servers "mysteriously" kept failing. When it became my turn to rebuild the fool thing I discovered it wasn't in our many-million-dollar server facility but down the hall from it, under a counter, plugged in next to a photocopier, big old laser printer and two fax machines. After discovering this and taking a look at the transients I'm was impressed they were lasting as long as they did. In your case hiding the problem with LCD displays isn't going to solve it.

2. On the other hand it could be lighting. Tube lighting flickers a lot and that can interact with the refresh rates on your monitors, particularly if you've all the same brand of monitors or your OS or staff keep setting them to the same refresh rates. Test this by adjusting the refresh rates of some monitors via software. Make one 65Hz, another 75Hz, if you can make another 85Hz. Also try working without the tube lighting. Get in some fill (torchier) and task (desklamp) lighting, preferably incandescent, and see if they obviate the problem.

3. So, if its not your eyes what devices are within 10m (same floor, floors above & below)? What devices are on the same circuits as your server? Are any of them motors, generators, heavy or intermittent draw devices? This includes laser printers, big fax machines, refrigerators, microwave ovens, etc. Survey all of this, ask your neighbors, ask to take a little tour for yourself, talk to the facilities folks.

4. Put servers on separate UPS's with power-line conditioning. It'll provide a backup to that generator (they know when to fail), clean up your supply, provide a bridge between the mains failing and the generator kicking in, just make everything a while lot more stable for your more expensive and critical hardware. Have purchasing get you a separate UPS/conditioner for each server and for heavens sake don't plug the monitors into them. If you really need server monitors when the power goes out get small flat-panel ones and plug them into their own UPSes (will give you handy spares you can sacrifice at need.) BTW these UPSes need not be power-all-day mondo models, just enough so that if that generator doesn't come on or there is some other problem they'll give everything time to shut down properly.

5. Replace the UPSes, "surge protectors" and the like every year or two. After enough hits the cheapie surge protectors become unresponsive and are essentially extension cords. The batteries on a UPS also age and start to loose charge faster. When you replace them migrate them down the critical path if you want but for heavens sake spray paint them, permanent marker them, something so they don't end up plugged into something really critical again.

6. Call an electrician. Seriously. 5 minutes with the hardware hanging from their belt and you'll have the comfort of knowing something. Also buy a compass, about US$15 or US$20 for a decent orienteering one. Walk it around the room to see if it shows any bobbles, it might help you track down the problem, or at least determine if the effect is strictly optical, electrical or there is a magnetic component too.

So between the time, services and hardware we're talking a few hundred bucks. Is that overkill? No way. That's popcorn compared to the disruption if one of your critical devices fails catastrophically, also nobody wants to work in a flickery environment. You wouldn't put up with a random "Feep" noise, why expect folks to deal with the visual equivalent? Staring at displays all day is tough enough without letting them degenerate into flickery ones.

Oh, and if nothing else works, remember the order of propitiation: Chicken, Goat, Virgin. If you ending up needing the last one call Corp HQ's IS, we usually have one or two on staff we could spare (we keep them just for this purpose.)

Re:2-phase? NOT! ...and safety

[Webmoth]

No, it is not two phase. It's single phase. Bear with me and I'll explain:

The power company transformer has a secondary winding with a grounded center tap. The voltage between the two poles of the transformer is 240V; the voltage between one pole ant the center tap (ground) is 120V. The grounded "neutral" wire is connected to this center tap.

If you hook up a scope between pole "A" and neutral, then hook it up to pole "B" and neutral, (providing the neutral is connected to the same pole of the scope) you will find that one is the INVERSE of the other, or reverse polarity. They are not 180 degrees out of phase, because YOU have reversed the polarity in hooking it up. Connect the scope between the two poles, and you will find a 60Hz sine wave of twice the amplitude (240V) as between one pole and neutral. There is no point to 180-degree 2-phase, because summed with cross polarity you get 0V and summed with same polarity you get single phase twice amplitude.

If there was a two-phase situation, you would see a sine wave that is the sum of two sine waves, offset by 120 degrees from each other. No point to this, because the resulting waveform is ugly and inefficient.

Three phase power is used primarily for electric motors. For a given power rating, a 3-ph motor can be made smaller and cheaper, runs cooler and more efficiently, and has greater starting torque than a 1-ph motor. Besides, a 3-ph motor can be reversed easily.

Occasionally in a commercial or industrial setting, you will find lighting which is "208" or "277" volts (odd numbers, hey?). This is because they are running from different legs of a 3-ph transformer bank than your ordinary stuff.

Back to the 1-ph system... it's not truly a neutral wire unless the loads on both poles of the transformer are equal. In a 120V circuit, it is NEVER a neutral wire because it is carrying current back to the power source.

In spite of the fact that the "neutral" wire (properly termed, "grounded current-carrying conductor") carries current, the potential between it and ground should always be zero. Anything else indicates a very serious and hazardous problem. If this center-tap wire fails between the transformer and your electrical panel, you may get a situation where the voltage between pole A and ground is greater than pole B and ground (depending on load), summing to 240V. This is a very dangerous situation (kills every appliance and computer and in the event of a ground lift energizes the metal frames of everything) and if you have it, turn off ALL POWER NOW and call either an electrician or the power company immediately.

Go off site

[Lxy]

Some evening after work, pack up your computer and monitor and bring it off site. See if it still flickers in a completely different environment. Either you have some electrical noise or you bought cheap monitors.