Why is it that pretty much every time a CRT monitor is turned on, it requires adjustments? Sometimes it’s only minor (eg move it a few pixels’ worth), and sometimes it is more (eg needs resizing by a couple of dozen pixels).

It’s easier to see if you adjust the screen to be as even and rectangular as possible, and take up as much of the visible real-estate as possible. When you then turn it on later, it might be too big or too small, or even not rectangular. (This may affect color, moire, convergence, etc. settings as well, but I have noticed it specifically with size/centering/shape settings.) The changes often reduce after the monitor has “warmed up” a bit, but it usually still requires some adjustment.

I’ve tried testing to see if I can narrow down the cause. Specifically, I tried turning the monitor off, waiting a bit, then turning it back on to see if it was changed. I also tried leaving the monitor on, but changing the screen resolution to see if it was the video card. Neither test changed anything—it’s likely the monitor, and only manifests when it’s been off for some time/cooled down.

I don’t know if it happens with LCDs as well, but I expect it occurs on either when using an analog source. And, for the record, this is not a monitor-specific issue because I have seen it on numerous monitors of different makes, models, and sizes—though the degree and frequency may vary.

I tried looking it up, but found nothing about what could cause a (analog?) monitor to require adjustments almost every time it is turned on (or even anyone asking about it).

  • FWIW, never seen it happen with LCDs, even on VGA connection. – grawity Jun 26 '11 at 21:49
  • @grawity, okay; that makes sense. – Synetech Jun 26 '11 at 22:36
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    There is still a CRT in existence? – Moab Jun 26 '11 at 22:37
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    @Moab, it may come as a surprise, but not everyone in the world is a rich North American/Englander. Not only are there still CRTs, but also VCRs and even non-electric, 1990’s-era cars; maybe even some shoes that are more than a year old. :-P – Synetech Jun 26 '11 at 22:40
  • Not to forget that CRTs are still used for example in video editing. – slhck Jun 26 '11 at 22:58

It has to do with the electron gun at the back of the CRT changing shape as it heats up. The electrons emitted from it follow a slightly different path as it warps, needing small changes to adjust the path of the beams.

TL;DR: Cheap electronics.

  • By the account, the screen would visibly change after some usage or on hot days. Also, wouldn’t it go back to looking like before once it’s warmed up? The difference do tend to reduce after it’s been on for a while, but if it does change, it usually stays different during that session. – Synetech Jun 26 '11 at 21:52
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    The "heating up" is hundreds of degrees. That would have to be some hot day to have any effect. And it could be that some of the changes become permanent, due to a shift in the placement of the electron gun from the heat. I'd look at getting a new monitor. – Ignacio Vazquez-Abrams Jun 26 '11 at 21:56
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    Wait, no I don’t think you get what I mean. I’m not saying that over the years, the monitor requires adjustment again; I mean that every day, when a monitor is turned on, the screen may be a few pixels to the left or a little bit too tall, then the next day, it might be a couple of pixels down or a few pixels to narrow, then a couple of days later… – Synetech Jun 26 '11 at 22:14
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    @Synetech inc. I'd say it's abnormal. From my experience, settings stay the same, once the CRT warms up. Are the CRTs all in same location? Maybe there's a strange magnetic field source? I have several old (some of them 18+ years) CRTs which don't show such behavior and while I used CRTs as my primary monitors, I never had such behavior. – AndrejaKo Jun 26 '11 at 22:37
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    @Synetech inc. Once the monitor warms up, it never ever ever ever and once again ever goes away form it's settings (unless it hasn't been turned on in say couple of months or so). I always payed much attention to having the used area completely cover the screen and on some monitors even 1 mm movement would be noticeable and I didn't get any. The 1 hour looks a bit excessive. I'm sure my monitors would warm up in less than 15 minutes even during winter. – AndrejaKo Jun 26 '11 at 22:49

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