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I've encountered this problem on several different systems with several different monitors: a monitor functions perfectly under Windows. I install a Linux and the max resolution is at some impossibly low value, mostly 640x480, changing it in Xorg.conf doesn't work. The X.org log file then shows that the driver cannot determine the correct refresh rate for the monitor, so it ignores everything in Xorg.conf and just loads in some default minimalistic mode. Googling the problem leads to an easy solution: set the HorizSync and VertRefresh in Xorg.conf, and everything works.

The problem seems to be a common one, and I've seen dozens of results recommending the solution. Each of them contains the warning that you should use the value ranges provided with the monitor. Because if you don't, and your video card sends a signal with the wrong refresh rate, this can damage your monitor.

Of course, you don't have a user manual for your monitor any more. If you are lucky to find one on the attic or on the net, it doesn't contain any information about the supported refresh rate. So you just type in the value suggested in the solution description, which varies wildly depending on your source, and cross your fingers. You restart, and...

... you've set the wrong values. So the monitor shows a short message like "input signal out of range", and you do a hard restart, repair your Xorg.conf in recovery mode, and everything is fine, including your monitor.

So does this warning reflect a real possibility, or is it just a geeky urban legend? Or is it something which used to happen in the past, before manufacturers started protecting the monitors against it? Is it technically possible with every monitor technology, or is it maybe something which can only happen to a CRT? If you think that it's true, why? Have you ever witnessed a monitor die from the wrong refresh config, or have you read of it in a reputable source?

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The short answer is - quite possibly. Don't push your luck.

Mostly, there are problems at scan rates which exceed the monitor's specifications (low or high). However, some poorly designed monitors or just a particular combination of events can blow a monitor with too low a scan rate or an absent or corrupted signal input. There was one case where a very expensive high performance monitor would consistently blow its horizontal deflection circuits when driven by a particular ATI video card. It turned out that during the power-on self test of the ATI BIOS, just the wrong video timing was being generated for a fraction of a second - but that was enough.

As far as scan rate limits, there is no way of knowing - it really all depends on the quality of the design of your monitor. Some will happily run continuously at 25% above specifications. Other will blow out totally at the first excuse.

The specification that is likely to be more critical is the horizontal rate as it probably puts more stress on the components than the vertical rate. I have found that as you approach the upper limits, there is a good chance that the geometric accuracy of the raster near the top of the screen may start to deteriorate due to lock in problems as well. However, it would be foolhardy to depend on this sort of behavior as an indication of going over the edge.

It will be much too late when you find out. If the manual says 75 Hz V and 64 kHz H, stay below both of these. If you exceed the safe ratings and the design isn't really good, there is the possibility of blowing components in the horizontal deflection and high voltage sections which will result in expensive repair bills. You will likely get no warning of impending failure. In addition, even if the monitor does not immediately turn into a pile of smoking silicon and plastic, components may be under more stress and running at higher levels of power dissipation. Total failure may be just around the corner. More subtle degradation in performance may occur over time as well.

You won't see the difference anyhow beyond 75 Hz and your programs may run slightly faster at lower refresh rates since the video is not using as much bandwidth (however, the difference here may be very slight or non-existent depending on your board, computer, applications, etc.).

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  • What about the problem you don't have the manual anymore and your monitor is too old for it to show up on any search. Is there any safe number you can try if, say, all you know is that your monitor supports 60Hz vertical?
    – Andyc
    Commented Apr 2, 2023 at 9:49
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Short answer: No, not with any monitor made in the past decade. And the monitors that this was possible to damage, were all CRT, it shouldn't be possible to harm an LCD in this way as far as I know. Nowadays if you send a signal that's too fast to your monitor (even on CRTs), the circuitry will detect that, and pop up a little box saying unsupported resolution / refresh rate.

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