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Why does my monitor sometimes turn purple?


I have an LG monitor and Windows XP Professional 2002 with SP3, AMD Centron Processor LE250, with a 2.19 Ghz 896 MB of RAM. Now I face a problem: my monitor turned purple. Occasionally, it goes back to normal, but most of the time, it’s purple. I use my computer rarely. There are no error messages, no magnetic fields nearby except speakers. Cables are OK. Please help me.

In this excerpt from 
Answercast #6
, I explore various hardware issues that would make a monitor turn purple during use. Unfortunately, hardware does go bad; so that is the first place that we will look.

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Check your connecting cables

Even though you say the cables are OK, I’m going to strongly suggest that you check them again. In fact, I’m going to suggest that you replace them or at least temporarily replace with them a borrowed cable.

There are two very common things that can lead to what you are seeing. The cheapest one to solve is the cable. So if it’s a cable problem, I really want to identify that first.

What happens is that either the cable itself is failing or the cable’s connection to your PC – or the monitor – has come loose. It may have come unseated and one or more of the little pins in there (the pins that make the connections, that skip the signal out to your monitor) isn’t connected or isn’t connected properly.

That can quickly change the color on your monitor, especially if it is a “sometimes” kind of thing. Just wiggling a cable a little bit can make or break the connections that cause that kind of a scenario. So do that first, get another cable. Make sure it’s seated properly in both the PC and the monitor and see if that doesn’t solve the problem. If it doesn’t, then I strongly suspect that what you have is a failing monitor.

Failing monitor

If the monitor is roughly the same era as the Windows XP you mentioned, it’s 10 years old. That’s actually not a bad lifespan for a monitor, especially an old CRT. So, the easiest way to test for this is to borrow a different monitor. Go grab a friend’s LCD monitor (or something that’s easier to carry over to your PC) and see if it exhibits the same problems.

If it does, then you know we’re talking about something entirely different. Then, you know you’ve probably got some kind of computer hardware problem with your video card or some kind of software configuration issue. Quite honestly, I can’t – I don’t a clue on that.

But what I really suspect will happen is that when you do this, the colors are going to be just fine. You’re gonna end up replacing your old CRT monitor.

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3 comments on “Why does my monitor sometimes turn purple?”

  1. I have a 32″ Vizio LCD TV that’s about 5 years old, which I’m now using for a computer monitor (since it has a VGA input). It also utilizes the Energy Star function that I can make it go into Standby after 5 minutes of inactivity. On occasion (rarely, fortunately) it tends to suddenly turn mostly green. Powering it off and back on again resolves the issue, meaning it’s a monitor problem. One time, when I rebooted the computer, the monitor would not display at all, just a black screen. I had to physically unplug and replug the power cord to correct the problem. Just a monitor getting old, is all. Of course, intermittent or defective cables, and pins or even computer video cards can also be culprits. But monitors do tend to go bad, and it’s not necessarily a function of the old XP days, either.

  2. If it is a CRT Monitor or a CRT TV being used as a monitor, this colour effect can be caused by the monitor not being switched OFF completely.

    That is, it is left either fully powered up or only down in to a Stand-By mode.

    Most CRT TVs and Monitors have a “De-gaussing” coil fitted around the display, with a Varistor/Thermistor in series.

    Just like the WW2 Degaussing coils fitted to ships, this is to remove any residual magnetic field.

    If that residual field is allowed to build up its strength, it eventually affects and deflects the electron beam from the cathode, to the extent of activating the wrong pixels in the RGB grouping, hence the change of colour.

    When the TV/Monitor has been switched OFF for some time, the Thermistor cools down and is close to a “short circuit”.

    When the TV/Monitor is switched ON, maximum AC current circulates through the Degaussing Coil, creating a strong 50 or 60 Hertz Magnetic Field, which kills the Residual Field.

    The Thermistor heats up relatively quicky, increasing its resistance, reducing the Degaussing Current & Field, to the extent that it has minimal effect on the Electron Beam; and the Residual Field has been killed off (temporarily!).

    Proper colours etc will then be displayed.

    But the Residual Field builds up slowly again, all of the time the CRT is operating.

    Hence the need to switch the TV/Monitor fully OFF, even possibly disconnecting from the mains supply for some minutes occasionally.


    Back around 1995, a colleague mentioned that he was observing such colour effects on the TV he had in his bedroom, making it “unwatchable”.

    On questioning him, he agreed that it was left in Stand-by rather than being switched OFF.

    I told him that he should switch it fully OFF several times that evening, waiting some minutes for the Thermistor to cool down, before switching ON again.

    He confirmed the next day that the colours had improved considerably, followed by further improvement over the next few days.


    Due to the different fundamental design with LCD and similar displays, it does not happen with them.

  3. To enlarge on my earlier comment, I first came across this phenomenem in the 1980s, when we were installing a large system involving many colour monitors.

    Previously all were “mono-chrome”, such as DEC VT100’s etc, where because the phosphor was uniform and did not have a “Colour Mask”, the effects would be very difficult to detect.

    Having demonstrated the need to switch the new colour monitors fully OFF to allow the degaussing to take place at switch ON, I also demonstrated the effects of the Earth’s Magnetic Field, by turning a monitor upside-down, keeping its screen in the more-or-less vertical plane.

    Normal way up – clean colours etc;

    Upside down – some fringing etc could be seen.


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