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Hardware

Flickering Monitors? 66

Posted by michael from the instant-headache dept.
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."
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Flickering Monitors? More

Flickering Monitors?

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  • Fans? (Score:3, Informative)

    by Stigmata669 ( 517894 ) on Friday March 22, 2002 @11:17AM (#3207152)
    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 (Score:4, Insightful)

    by crow ( 16139 ) on Friday March 22, 2002 @11:20AM (#3207172) Homepage Journal
    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 (Score:3, Informative)

    by President Chimp Toe ( 552720 ) on Friday March 22, 2002 @11:23AM (#3207193)
    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!
  • I lived in a place for a while where if the monitor was set to anything above 60Hz the screen image would waver back and forth quickly. We tried everything we could. The house was old so we ran some new electrical wire. The breaker box was new and properly grounded as well. There were no visible major power lines around the place. Some of those high power lines can cause interference. I don' think there was a cell tower nearby either. The only thing I can think of was that there were railroad tracks running behind the place. Its possible that the railroad were sending radio communications and interfering that way. At the time I lived there I didn't have a UPS but my brother whose house it is has one now and it doesn't seem to help.
    • I have this exact same problem. I've given up and resorted to using 60hz refresh only. I checked for lights, moters, dirty power, everything. Remember, this isn't really flickering, this is a kind of shaking. Your eyes will filter it out if you're using a black background, but it's unbearable if you're trying to do anything other than watch a dark movie from accross the room. (I have a 19" sony trinitron in my living room)

      Oh, and ALL my monitors do it, 14", 17", 19", cheap to midline to pricey. They also do it in ANY room.

      I really wish I knew what caused it... I'm ready to move soon though, so hopefully things will be better then.
    • Samus writes:

      The only thing I can think of was that there were railroad tracks running behind the place. Its
      possible that the railroad were sending radio communications and interfering that way.

      A friend of mine has the same problem, and he also has 'light rail' (Metra tracks) about fifty feet away.


      The 'screen shake' is a constant problem, there is also wide-spectrum 2.4Ghz interference at regular intervals, coincident with the passing of passenger trains.

  • My desklamp is a neon, and it's just above my monitor. Whenever I light it, even if I'm at 800x600@100Hz, it will flicker. So I never use it (prefer ambient light).

    I also whitnessed some speakers doing some weird things to monitors. Another thing to check for.
    • the flickering i think has somthing to do with the fact that the neon light (prob. 60 hz) and the monitor are "blinking" out of sync, giving you your headache (pun intended). much like tv's having "black stripes" on tv, if the tv isn't synced correctly.
  • I'm experiencing a related problem when somebody turns off the light (a fluorescent tube - hope that's the correct term, the dictionary says so ;-) in another room, the monitor flickers for the portion of a second. I guess this is caused by a voltage spike that appears when the light is turned off.

    Regards, Specialist2k

  • Your not going to like this. (Score:1, Interesting)

    by Anonymous Coward
    Any of your questions could be the culprit, and if that is the case, a separate UPS for the monitors would likely fix the problem.

    But you don't say what type of monitors these are, or their age. Which brings us to the question: ARe these just crappy, cheap monitors?

  • UPS will help if it's not magnetic (Score:4, Informative)

    by Snowfox ( 34467 ) <snowfox@NOsPaM.snowfox.net> on Friday March 22, 2002 @11:53AM (#3207385) Homepage
    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.

    • I think the power in my apartment is like this.

      My monitor is "wavy" (I've tried 3 different ones), and I had one die. My DVD player is flaky (crashes regularly, locks up, etc), and I have a PC that just dies once every couple weeks for no reason.

      I'm afraid for my current hardware. My DVD player is permanently damaged (it's at my Girlfriend's place now, and still locks up...), and one of my monitors just snaps and dies all the time (hard power interruption fixes it temporarily. I wonder if I can hold my landlord responsible for damages?

      Do you have more details on what bad power can do to electronics? (quared/spiked/etc?)

      I'm moving in July (on Moving Day, here in Quebec), but in the mean time, I just can't afford to replace my gear.

      S
      • Here in the states you can request your power utility to come out and do tests on the electricity coming into your place of dwelling. The place I'm moving out of here had one grounded socket in the entire apartment and it wasn't even in the bathroom. 2 weeks later with the threat of putting us up in a hotel looming the landlord rewired the entire building (we were the 4th tenet to complain). Get documentation from the utility company if you want to pursue this.

      • I think the power in my apartment is like this.
        My monitor is "wavy" (I've tried 3 different ones),

        OK, I confess. I live in the apartment next door to you and I've been running a 20kV Van de Graff generator alongside the superconducting magnet that I keep "Frank" in.

        [All kidding aside, my boss at the consumer electronics store told me to do this for a few weeks to drum up some business for new TV's, computer monitors from my neighborhood.]

      • Do you have more details on what bad power can do to electronics? (quared/spiked/etc?)

        No specifics, but I'd wager a question posted to sci.electronics.repair would net you more replies than you can count.

  • I had problems at a lan party that was finally traced to my monitor cable running too close to several power cables.

  • Good be power (Score:2, Informative)

    by netringer ( 319831 )
    I would check for power problems. I once had a similar situation, where you could actually hear something when the monitor screens would shrink a bit. One quiet night I figured out that it was the power hungry Sun SparcPrinter on the same power circuit that was firing up the fuser periodically. It was causing brown-outs.

    If all of your flickering monitors are on the same circuit, or worse, the same surge protector, try changing that.

    I have had surge protectors that were "used up" and were spiking the power on their own. Try taking the surge protectors out.

    You might try monitoring the power voltage with a mulitmeter to see if you see a change when the flicker happens.

    Try testing with a small online UPS for one monitor to see if that cures the problem. Note that it cannot be a standby UPS. Those won't cure brown outs. http://www.pcguide.com/ref/power/ext/ups/types.htm [pcguide.com]
  • I've got the same problem in my basement, but I've also realized that 2 things are causing this issue:

    1. Bad Ground/Non-existant ground. Take a good APC surge protector (mine has a little red "ground fault" light on it) and test the outlets/curcuit that the monitors are plugged into. If that light lights up, what could be happening is that you're getting a power drain through ground (or no ground at all) and the voltage on the "neutral" side can be varying.

    2. Overloaded phase on 2 phase ??? (House Wiring) -- A friend of mine explained to me that since there are 2 phases in house wiring (may not apply to your SB office) if you overload one side, you could cause fluctuations in +V on the other phase. I tend to believe this theory (in conjunction with my other problem) causes flicker on my monitors; when the furnace + washer kick on, the flickering gets worse.

    That's my personal experience -- hopefully it helps.
    • All of the office equipment will be 2-phase. Three-phase wiring is mostly used in industrial settings, although it might also be used with consumer oven and electric clothes dryers.
      • 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.
        • Just so you know, two things you said contradict each other:

          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...carries current, the potential between it and ground should always be zero.

          If its carrying current then there will be a potential between ground and neutral, which is the real world case. BTW, neutral and ground are bonded together, once and only once, usually at your circuit box. The neutral is very close to zero, but never zero for loaded circuits. Secondly, an ideal 3 phase motor would not return any current on the neutral, but they don't exist, so in three phase, there is current on the neutral, granted very small, but still there.

          A side note: In a three phase system, neutral lines used to be sized to the same gauge as one of the phases, but things like computer switching power supplies, produce harmonics on the line which would add together on the return from the three phases and burn out the neutral, so now they are sized larger.

  • Unless you've got a generator running contiunously, or a battery based online UPS for the entire building, you can't assume the power is truely uninterruptable. I'd put UPS on everything as a matter of course, so when you get that few second outage when the generators kick in, you don't lose everything.

    --Mike--

  • Buy a small UPS and try it. If it doesn't help, return it.

    What ever happened to experimentation, isnt' this part of the scientific method? :)

    • Be aware that most cheap UPSes (Uninterruptable Power Supplies) are actually SPSes (Standby Power Supplies) and only provide basic spike/noise filtering when normal AC voltage is present.

      A true UPS (such as the 1KVA Siemens that sits under my desk) converts the AC voltage to DC then runs it through an inverter to create a rock-steady and smooth AC output. It doesn't matter what comes in on the mains side (short of a direct lightning hit), the output side is clean as a whistle.

      If you want to get rid of low-frequency voltage/phase fluctuations on your mains supply then you really have to use a true UPS or at least a big, heavy, ferromagnetic resonator.
  • I'll bet it is magnetic interference. One of my old offices was near a generator, and the monitor would go crazy all the time.

    My friend's got this device that you use to amplify a telephone. You can also use it to listen to EM radiation -- put it near your monitor or electrical wires and hear a nice hum. If you get one of those (I'm sure they're pretty cheap) and hear a hum in the middle of your office with your equipment off, then you'll know you've got a problem. ;)

  • You might try... (Score:2, Informative)

    by OneFix ( 18661 )
    Something like This [advancemag.com]. It might be cheaper to begin with and it's not another component to go bad :)

    There are other similar products, but that should give you a good start.

  • Looking with the right tool (Score:4, Interesting)

    by martyb ( 196687 ) on Friday March 22, 2002 @12:48PM (#3207738)

    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 (Score:5, Informative)

    by maggard ( 5579 ) <michael@michaelmaggard.com> on Friday March 22, 2002 @12:50PM (#3207751) Homepage Journal
    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.)

    • great advice, however, Id like to add that in addition to flourescent lights flickering -- the power transformers in flourescent lights (rectifier? I can't recall the name) produce an EM field that oscilates at the same frequency. This field can make a monitor very *unuseable* if its near enough to the field.

      • Re:Step by step (Score:2, Interesting)

        by aethera ( 248722 )
        i once visited a scene shop in the theatre of a local university and the technical director there showed me one of the most dangerous things I have ever seen.
        They had an older style table saw, the type that rarely has a blade guard (nor can you use them anyways when ripping an 8' piece of ply). He powered it up once, it ran normally. He turned it on or off a couple more times, and finally said "Got it". Though I could distictly here that the saw was on, the blade appeared not to be spinning. When he slid a two by four into the blade it slowedthe rotation down just enough that you actually could see the blades turning, though it was in a funny oscillatiion, like dancing in a high speed strobe light. Turns out, the flourescent lights flickered at just the right frequency to make the moving blade appear to be standing still.
  • First of my guess would have been proximity, but you stated that you'd tried moving them appart. What happens when only one is plugged in? Do you still see the effect?

    Odd as this may seem, I've found on more than one occassion the ole' HPLJII's (and a few variants) have a horrific draw on the power grid every few minutes. Something to do with keeping the internals to the right temp or somesuch. Anyway, yank the power cords of any printers you have in the nearby vacinity.

    You'd be surprised...
  • and it was due to proximity to the big APC ups's and their tranformers (or whatever was generating such a strong magnetic field).

    my solution: convert to lcd displays. I am now using a pair of 'old' SGI 1600sw displays and obviously all my flickering is gone. before I used a pair of dell/sony 20" monitors and the shaking (not really flickering) just drove my eyes nuts.
  • Place each monitor in an appropriately sized six-sided grounded metal box with a small hole just big enough for the power and video cables.

    This should elimiate your magnetic interference problems. I would also recommend the chrome option for a really classy look.
  • In one of the buildings that I worked in, my monitor kept flickering no matter what I did. Regular monitors (Apple, SGI, Sun, Sony) were all but unusable. The only monitors that came close to being usable were old IBM Trinitron monitors that were bought with old IBM RS6000 320's and 340's. These monitors weighted 100 lbs or so and probably had significant sheilding. Additionally, it may have been the BNC cabling. We tried UPS's and other power conditioning to no avail. We tried bringing in power from other rooms, no luck.

    At any rate, after much eye pain and quite a few hours of tracking the problem down, it was found that one of the main power lines for the building was in contact with the metal frame of the building near that office. I guess that it was producing a 60Hz oscillating electric field and that was messing up the monitors. At any rate, when that power line was fixed, the monitor flickering went away.
  • that is is EM radiation.
    Want to know how to check?
    See if your balls are shrunken!
  • First of all, you almost certainly need to invest in either a voltage regulator or a UPS (which will perform the same function) to clean up the power going into your monitor/machines.

    Secondly, check the proximity of items that are very high voltage and contain magnets. Something missed by a lot of people that can cause this problem is the proximity of your speakers/subwoofer to your monitor. I have a 21 inch ViewSonic monitor and a set of Klipsch ProMedia 4.1 speakers and they don't like each other very much when they get too close together.

    Cheers,
    Blake
  • One of my clients (a large law firm) had a user who seemed to be death to monitors. They tried new monitors. They tried new video cards. They tried a new computer. They even tried moving her to a different office. Monitors still died.

    One day, they called me and said "the monitor flickers." I went over there, asked some questions, and found out that the monitor has ALWAYS flickered, but it just now started to drive her nuts.

    So I turned off the typewriter that was next to the monitor (which stopped the flicker) and told them that the typewriter (which was always turned on and always next to the monitor) was the likely perpetrator of death, and physically separating them was the only solution.

    Another client, a large print house and manufacturing facility, has a few which flicker whenever a machine starts up.

    In your case, unlikely it's the backup generator, because it's not running all the time.

    If the problem is indeed in the power, you'll need to get a power filter. What that does is takes dirty power and gives you a nice, smooth, clean 60Hz (or 50Hz in Europe) sine wave.

  • Does the flickering go away when you stop eating crunchy foods? If so, then I've got an idea what might be causing this...
  • The building has a backup power generator thus we didn't see the need for a UPS.

    Anyone else find that funny?
  • One thing you may be able to try is powering down EVERYTHING in the building... and I mean everything: water heater, coffee pot, alarm panel, wall clock in addition to the usual lights & computers. Unplug other computers, monitors, small appliances, and TVs. Turn large appliances off at the electrical panel; some have transformers and electronics that remain energized when you hit the power button. Remove battery powered devices like cell phones and PDAs from the building. Well, maybe you'll need a flashlight, but it will be pretty easy to tell if that's the culprit.

    Leave the computer and monitor in question on, though. Does it flicker? If so, problem is external to the building. No? Start turning things on one by one, checking the monitor every time. If it's one thing that's doing it, this should isolate the problem.
    • I forgot one thing that can be a big problem: Dimmer switches, especially if they are the cheap SCR hardware-store variety.

      Do this first: Turn them all the way down/off and see if your problem goes away. Cheap SCR dimmers are *the biggest problem* in causing noise in audio systems, that's why you never find them in radio stations, auditoriums, or recording studios (they've got mucho-buck lighting control systems that don't put out dirty-waveform EMFs).
  • The gen set is great, but what about the lag time between power failure and generator startup?

    You need something to carry you through. A UPS is great for this. (Now if you have a whole-building UPS for this purpose, that's great.)

    What if the gen set fails?
    • A UPS for a whole building would work great for preventing panic during outage crises, but I'd recommend UPS units next to the boxen. Reason why is that I have often seen breakers trip for computer rooms.

      All too often I have seen what was a small server room expand with hardware upgrades and with no forsight to include upgrading the wiring. That poor 20 amp breaker eventually will be a rude awakening to those who didn't want to include the time of an electrician into their plans.

      I feel a local UPS in addition to the other larger backup power generation is a great idea. They are small, easily servicable and replaceable by just about anyone; whereas a failure of a large UPS may require a service call.

      I once had the pleasure of being close to a large 1.6MW Cat twin turbo diesel generator when it decided to toss a valve out of the cover. A few hundred hours of operation into another shift, the shaft between the engine and the generator snapped. Nothing like 2800 horsepower wanting to be free once in a while... After several years, the nicad battery pack failed to turn over the two starter motors. They were replaced by a pack of lead acid batteries (cheaper, but an expected life 3 years.)

      While the large sets are lifesavers, they can have extended downtime due to their size. They seem to work well in addition with small, replaceable UPS units.
  • Look for Two-way radio's and Cell Phones, or another client in the building with radio equipment. I get speaker pops and monitor shake when some cell phones are used near my monitor and speakers. We used to be able to reboot older Compaq laptops by just keying up a two-way Motorola radio. If my buddy on the other side of the cube pissed me off I would just hold the radio to the side of the cube wall and key up. His laptop would just spontaneously reboot itself.

  • Go off site (Score:3, Insightful)

    by Lxy ( 80823 ) on Friday March 22, 2002 @06:38PM (#3210215) Journal
    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.
  • A plugged in electric clock caused the monitor to flicker. When I moved it away that stopped it.
  • That we finally determined was being caused by some regular electrical wiring in the wall directly next to the monitor! Moved the monitor to the other side of the desk away from the wall- problem fixed. In any event, its definitely interference from somewhere- just finding out where can be a bit of a headache.
  • You still need a UPS. A backup generator can't start up fast enough to keep your systems running in the event of a sudden blackout or brownout. An active UPS produces incredibly clean power and eliminates even the slightest hiccup if your generator needs to start up.
  • With all this discussion on using a UPS to reduce line noise it's worth pointing out that most of the low-cost UPSes on the market are actually SPSes (Standby Power Supplies).

    Until such time as the mains voltage drops below or above the trigger level, they're nothing more than a medocre spike supressor and filter -- just like the low-cost spike supressors you can buy inside power-boards.

    A true UPS runs a full-time inverter.

    Incoming mains power is rectified, smoothed (turned into steady DC) and then fed into an inverter that creates the AC waveform which is used to power your computers etc.

    Short of a lightning strike, nothing that happens on the input side will affect the output waveform.

    Spikes, voltage and phase fluctuations are all eliminated when the AC is converted to DC inside the box.

    By comparison, the cheap SPSes (erroneously refered to as UPSes) simply pass the mains voltage through a crude filter and spike suppressor unless they're triggered into inverter mode.

    Another problem with these cheap SPSes is that they often don't play nicely with low-cost generators.

    I used to have a 600VA SPS that I used on my PC but found that the power outages I was getting were often an hour or more in duration (I live in the countryside where trees regularly fall across the lines).

    To solve this problem I bought a 2KW Honda generator but found that when I plugged the SPS into the generator it would repeatedly kick in and out every 2 seconds or so. Turns out that most SPSes are very sensitive to the frequency of the mains and most small generators tend to have a frequency variation well outside the SPSes acceptable limits.

    Some better SPSes (such as the APC line) have an adustment so that the sensitivity to frequency fluctionats can be reduced but sometimes even this isn't enough if you're running other loads of the generator.

    That's why I bought a true UPS. You can feed it anything and it just keeps putting out a nice smooth, superbly regulated AC waveform. By going up to 1KVA I also obtained an extra 15 minutes of operation on batteries so I don't have to rush to get the generator out and started.
  • Dint't see anyone mentioning this, but aren't your desks by any chance fancy ones with motorized control? You have a control that makes them higher or lower, among other things? I've had that problem in my company, where engineers loved those desks more than mom, and monitors would simply flicker from being near the engine under the table. I told them to fix the tables to their preference and then unplug the engine from the power socket.

    /Pedro
  • most of the comments on this discussion have delt with em interference of some kind. i bet that this is indeed the case, if you can't get rid of the interference, you can block it quite easily. one thing we do with sensitive scientific equipment is to put it in a faraday cage. this is just simply a metal wire cage. em interference cannot penetrate a conductor (as long at the spacing between the wires is smaller than the wavelength of the interference - the interference you're getting is probably on the order of 1 meter or longer, so you have nothing to worry about). you should be able to get away with a cage the covers the back and sides of the monitor - it would be kinda useless to cover the front :). if you know where the interference is coming from (i.e.wires in the wall), you can just block the source (put a mesh between the wall and your monitor). hope this helps.

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