Why would a CRT monitor stop displaying higher resolutions for one computer?

Question

I have problems displaying resolutions above 640x480. Until recently the very same computer, graphics card and monitor used to operate just fine. On another computer the monitor still works as expected.

I recently got a new PC, and up until now there has been no problem switching between my old PC and new one with my Dell monitor (and keyboard/mouse/speakers). All the parenthetical items work fine, but my monitor now refuses to display on the old PC unless I boot in VGA mode. Both are running through video cards, but the older PC refuses to display any resolution above 640x480. I can't imagine what could cause this issue - I haven't changed or installed anything since the last time I used this monitor with the older PC. I have been able to switch between the two computers with no problem previously.

Answer 1

It sounds like there has been a hardware failure in the video card of the old pc (not the monitor).

Not a catastrophic failure, but some component necessary for generating higher resolution video signals.

Higher resolution implies higher frequencies. It's quite plausible that the failure only affects higher frequencies.

EDIT: I'm thinking of a failure in one of the chips used on the video card. I'm not sure you'd call it 'infant mortality', but I work in the chip-making business and I've seen partial failures like this before.

EDIT2: Chips may have incipient faults which show up at times of stress, such as turning the power on. It seems like a coincidence because, well, coincidences sometimes happen.

When we test devices, we have to check all functions because defects can make some functions fail while others keep working.

Answer 2

Maybe the higher resolution video modes are set to too high a frequency?

A relatively new video card like the 8400 could easily send 1280x768 at over 100hz for example, and old crt's may not be able to handle that. VGA mode is 640x480 60hz, try keeping the refresh rate at 60hz as you increase the resolution.

Edit: Obviously you should only keep the refresh rate at 60 hz as a troubleshooting measure, if you discover that it works, then you should increase the refresh rate to a more comfortable level.

Answer 3

I truly doubt this is the case (and most often, this requires some human intervention), but: any chance your new computer somehow (and erroneously) updated the EDID in the monitor? Or: any chance the Display Data Channel (required for EDID) is broken in the cable or connector? (You're not using a KVM switch, right?)

Some monitors come with wrong factory EDID information, which then basically prevents one from selecting some resolutions or frequencies in the OS's display settings. For most systems these are just annoyances, and fixing the EDID then merely makes workarounds like "show incompatible video modes" no longer necessary.

In your case, you can in fact still select the very same resolutions that used to work just fine. But maybe the OS now thinks that this resolution allows for a higher frequency, or for non-interlaced operation while the monitor in fact does not support that?

Maybe software like Monitor Asset Manager 2.3 can provide some information? That will show you both the information provided by EDID, and the information that Windows has stored in its registry. If those are different, then maybe you can do a "detect monitor" or "detect screen" on your old computer? (For the sake of troubleshooting, I would first copy the information from that software before running any monitor detection again.)