Hunting down who a monitor (or sometimes two) goes blank
 

I am running Slackware 14 with three screens, using KDE.

The issue I have is that all three display ports seem properly configured, and have worked for a couple of years, and all of the sudden the last several days, mid-day, something happens and one or more screens go blank.

Looking at messages and syslog, I don't see anything unusual. Can someone point me in the right direction towards figuring this out?

egrep -i "fail|warning|error" /var/log/Xorg.0.log

Done. Nothing.


Happened a couple of hours ago again, and this time I caught a KDE daemon message. Things restored to proper operation.

It happened again. This time it came back. There was something flagged for audio. I am wondering if there is a display card or MB problem.

No relevant log messages.

Let's do this the easy way, next time it happens as soon as it comes back, open ksystemlog (just type it as one word). One of the really nice features of KDE is their log viewer
You have a choice of 5 logs to choose from
System
Kernel
Auth
Daemon
Xorg
I'd start with Xorg log, scroll to the bottom and see what it says, it doesn't have a time stamp associated but the rest of them probably will. Check the time stamp on the entry, does that match up with the event? The logs are chronological so if you note the system time upon occurrence you can go back and find the event in the log.

I was just tailing the logfiles. But the opportunity to learn a new tool presents it self.

Three occurrences I saw today. I had other things that were pressing so I did not investigate, but the logfiles I was tailing showed nothing of note.

If I disappear for a couple of days, it doesn't mean anything. I have relatives in the hospital, and another one going in for surgery. It just kinda all piles up at one time, and my workload got real high real fast.

No problem, I'm subscribed to the thread. I hope everybody is feeling better, catch you when you have some time

The problem is that the graphics processor on the MB is intermittently dying. The other two monitors stay alive because they are running off a video adapter.

I have cleaned dust off the MB, and reseated the CPU, but no joy. Vibration doesn't seem to make the problem come or go. So I guess it is a live with it.

The tip to look at the Xorg files made the debug go smoother.

This is a late post, but may help someone who ends up searching for a similar problem.

MB is a Gigabyte Z77-D3H, with an I7-3770.

You also might check the cabling. Sometimes wiggling it fixes this type of intermittent problem. If it does, then the actual problem is corrosion/oxidation on the contacts. Exactly why the display goes blank can vary. With the VGA cables it is usually the sync signal that is lost. I'm not familiar with the signaling of HDMI or DVI cables to know wit those.

It also happens to my crappy videocard Radeon HD3470 not being able to pump enough amps. This happens especially during cold startup. I just turn the monitor off and on and get done with it.

If you don't want any monitor to ever blank.

$ xset -dpms s noblank s noexpose

I tend to have this always set and push buttons on the hardware when I walk away for any duration. Although I suspect a hardware issue. PSUs tend to degrade over time and if you don't have a 200W buffer above your actual needed specs it could degrade to under spec in spite of what the sticker says. And LCDs tend to degrade, I seem to have issues at 3+yo and have replaced almost all non-CRT displays in less than ten years.

Shouldn't... unless it is a CFC that is failing. Out of 3 I've only had one die - and that was because the power supply in the LCD died. Laptops on the other hand... two - and both were the CFC backlight. Found that out by taking an LED flashlight and putting it flush against the screen. The area around the light showed the display working just fine - but the backlight was out.

I have an old P4 dell that has a burnt out backlight. The VGA out still works though. I keep it around because it has a working optical drive and can act as a wifi bridge / router in a pinch. I don't buy a laptop that doesn't have external monitor support. Of the screens that I've had fail, one that is in process now buzzes after a relatively short time on. The other wouldn't show a screen, except with some effort and luck, Cntrl+Alt+F1, then Cntrl+Alt+F7, over and over until the screen magically worked. It probably had more to do with the nVidia integrated GPU. But it did eventually stay invisible. A new screen had no such symptoms. But at that point the base system was old enough to warrant a change.