04-07-2010, 07:07 AM

This is so weird I don't have a clue what to do.

I've got a G5 with a couple of 23" monitors. Everything works great... I can leave the computer running for hours or even days and there's no problem.
For instance, I can leave Safari running, go away for 2 days and come back and it's still running great.

If I open up a movie on YouTube however, or run a screensaver... at some point, both monitors will suddenly go completely black (as in, completely shut off so that the white power lights come on). The computer keeps running as if nothing has happened and the movie keeps running in the background.
No matter what I do though, I can't get the monitors to come back on.

The only choice I have is to do a forced shut down using the power button.

Then I have to wait at least 15 minutes before attempting to start back up again or the monitors still won't work.
Once I wait for 15 minutes, I'll start it up.... the right monitor comes on ok... then the left one stays black for about 10 minutes until it too finally comes on.

So.... what the heck do I do to diagnose this problem?

04-07-2010, 10:59 AM

Never heard of anything like this, but it may be the video card. Did you upgrade it recently to a flashed model per chance?

04-07-2010, 11:16 AM

Nope.. the only changes I've made since I bought it a coupla years ago was to upgrade to Snow Leopard. Until then I had no problems. I was thinking it might be the video card as well but I wish I could confirm it before spending $500 on a new one.
The thing that confuses me is the fact that it only happens when I'm watching a video or running a screen saver. If it was the video card, you'd think it would keep happening constantly no matter what program I was running.

04-07-2010, 11:35 AM

Is this a G5 or a Mac Pro? You said G5 in your first post, in which case it won't run snow leo. Since your monitors are both doing the same thing, it's doubtful that both monitors are bad. The commonality with both is the video card. Check for a firmware update on your board (should come through the apple software update). Also, grab the latest combo update from the apple site for your OS.

04-07-2010, 11:51 AM

Sorry, yeah it's a Mac Core 8. I keep calling it a G5 for some dumb reason.
I'll give the firmware update a try... hadn't thought of it. Many thanks for your help.

04-07-2010, 01:20 PM

Energy savings settings turning the monitors off? Troubleshooting always starts with the most basic, obvious stuff. So that's where I would start.

04-07-2010, 02:58 PM

I suspect that the card may be overheating under the additional load that the video/screen savers are putting on it.

The key here is that you're having to wait 15 minutes or so. That would give the card enough time to cool down so that it begins working again.

You don't mention what type of graphics card you have but if it has one, check the cooling fan on it. Also, right after the monitors go blank, place your hand above the card. Do you feel a great deal of heat coming off it?

If it is over-heating, then you'll have to replace it because it's life-span has been greatly shortened and it will eventually fail entirely.

04-07-2010, 05:19 PM

Yeah, that kinda makes sense. It's not a simple thing like the energy savings or anything cause all that stuff is turned completely off.

The only time it seems to happen is during extra video usage... although even then it's still so random that I could spend hours watching videos or the screen saver could run for a coupla days before it finally just shuts off.

Like I said... totally bizarre. Guess my only choice may be to get a new graphics card and see if it solves it.

Just outa curiosity, is it possible that the Activity Monitor or Console Messages app might keep a diagnostic record of this happening?

04-07-2010, 05:36 PM

SoaringDodo has hit it. The video card is overheating.

My guess would be that the fan for the video card is getting clogged with dust. You might want to take the video card out entirely and give it a good going-over with some compressed air.

Or simply look at buying a newer video card. They can wear out over time just like anything else in the computer.