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I've got 2 computers whose CRT monitors, one 15 inches, the other one around 22", are sitting right next to each other. Both computers and both monitors are plugged into a single power strip that's plugged directly into a wall socket. Whenever I switch one on, the other one flickers momentarily. I originally thought that this was a harmless phenomenon, but so far I've had to replace the second monitor twice. I took one of the broken monitors to a local electrician and he said that the power supply had failed and managed to fix it for me, and I suspect that it's the same deal with the other broken one.

I remember reading something a long time ago that said that when CRT monitors are switched on they draw a lot of power. Is there any truth to that? Could that be what's killing the monitors? If it is, what sort of equipment should I invest in to keep this from happening?

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I can't believe that its now been so long since CRT monitors where commonplace that we're now talking about them like they are ancient artifacts. Actually, I can't believe you were able to replace one of them twice without upgrading to an LCD. Are you a graphic artist? I heard that some people need to use CRTs for special reasons like color correction. lajuette's answer is right though, its normal for one monitor to interfere a bit with the other one when you power them on. – deltaray Nov 21 '10 at 15:41
Nah, i'm not a graphic artist, I just have a bunch of old CRTs I'd like to put to to good use. I do play a lot of games, and while LCDs are nice they tend to look like crap when running at non-native resolutions, so CRTs are great in that regard. – cornjuliox Dec 12 '10 at 11:02
up vote 3 down vote accepted

A CRT monitor uses a magnetic field to deflect an electron beam. The beam hits the end of the Tube (the part of the display you are seeing) and illuminates its surface.

When you power on your monitor it distorts the magnetic field around it because it tries to get rid of magnetic distortions (see Degaussing in this article). If there's another CRT monitor nearby its electron beam will be deflected by the fields it controlls itself AND by the distortion created by the other monitor. After a few seconds the fields stabilize and everything should be fine again. That's it for the flickering - it's normal.

I don't know for sure if powering up a CRT display is drawing that much of power, but i'm sure that's the case. Maybe you should try to use two different wall sockets? Getting a better power strip might help, too (some have extra functions like overload protection).

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I would recommend getting a circuit tester to make sure something isn't mis-wired. I once had a power strip that had hot and neutral reversed and it blew out a couple of monitors. Test the outlets in the power strip as well as the wall outlets.

Circuit Analyzer

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Well, I don't think anything is miswired. It didn't pop or anything as soon as I plugged it in, it worked for a few months before it conked out. A circuit tester sounds useful, so I'm definitely gonna invest in one of those and learn how to use it. – cornjuliox Nov 21 '10 at 20:08

CRTs use high voltage internally and when turned on will draw a big current as the coil loads up. It's not likely (but is possible) that this is killing the other monitor. Remember that CRT monitor power supply failures were VERY COMMON. If the monitor is over 5 years old and still running on its original power transistors then you got a good one. I've had dozens of CRTs die from power supply failure - but usually it was after they were aged to a point where it was cheaper to replace than repair. If you've got a great monitor that's worth repair, expect to pay 50 to 75 dollars ($US) to get it repaired - if you can find someone who still does it.

The answers about degaussing sound good - but remember than lots of lower priced CRT monitors did NOT include degaussing capability. If your second monitor doesn't degauss on startup it may be that the current draw from the second monitor is causing the voltage into the first to drop low enough that it has a momentary "blip". It may be noticeable but should not be enough to damage anything. After all, you turn the thing on and off without damage many times during the life of the product.

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it seems like cornjuliox really likes his CRTs -> graphic designer? high-end user? IMHO likely it's the degaussing. But then i believe he should know how his tools (monitors) work... – lajuette Nov 22 '10 at 6:07

This is caused by the auto-degauss on switch on. Most CRT monitors have a coil surrounding the screen (this is definitely not a deflection coil). The purpose is to nullify any magnetic field that may build up in the metalwork supporting the CRT. What you are seeing is the degaussing coil on one monitor causing a shimmer on the other.

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While quite possible it is not guaranteed to be the cause. Lower priced monitors often didn't have the degauss option. – hotei Nov 21 '10 at 20:02
I've seen it before so I'd say it was more than quite possible. – Tog Nov 22 '10 at 7:51

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