iMac 27" Screen goes black repeatedly, but then settles for a while?

Well finally some good news! The iMac seems to be working fine after they put a 2nd new video card into it. I've been running it for a day now and no problems and the screen is extremely sharp and clear.

Recall the first time they replaced the video card it wound up with a bad case of pixelitis ( new word I just invented ) and their fix was to just get another card from Apple and replace this one. It makes me think the video card design may be on the ragged edge or there was a issue with some of the card components.

That's all for now but I hope this has helped some of you in figuring out your issues.

CU

Jim

I had a similar problem with mine as well. I've had the iMac for 8 mths. The screen started flickering and then this past tuesday, the left side of the screen went a lot darker than the right side. I called apple and after some troubleshooting (which didn't work) I had to take it in where they replaced the LCD screen.

I too have been having the same problem. I had our local mac guys check it out and as I expected nothing happened.

But it made me think what has changed? And then I realized that my business partner added another computer to the same power circuit.

So—I now have had it on its own circuit without issue. So I spoke with the tech and he did agreed that the crash makes sense now and that it would be caused by lack of power.

If this helps.

Hi Slugtcao

I have serious reservations the 2nd computer on the circuit is your problem. For another computer to be on the circuit drawing maybe 200 watts to cause a problem would suggest a very serious wiring problem that would show up in some other manifestations such as circuit breakers always tripping or other serious desk lamp dimming etc.

Given what I found on mine, I.e., a bad video card, it would seem your issue is the hardware of the computer and not the line voltage. I might note that mine took a period of several weeks before it became consistent enough in its failures for me to decide something needed to be done.

Of course there are always things that defy common sense logic but I think the line voltage is an issue that, although not impossible, is of almost non existent probability.

Keep us tuned in to what you found

Jim

Maybe I forgot to mention that we have 3 27" iMacs all running through a 400w UPS. Then in comes the MINI and then I had issues. I worked today…all day…without issues. And all I did was take the mini off the UPS.

All day...no issues.

Hello again Slugcato

According to the Apple site the new 27" iMac's draw a maximum of 310 watts and the miniMac draws a maximum of 85 watts which is 1015 watts plus the monitor for the miniMac. This is still below the maximum you might expect from a normal house breaker which can easily support a 1500 watt hair dryer and should actually handle over 1700 watts before a breaker would start to trip. The fact you have a 400 watt UPS is of no consequence unless you have a main power interruption in which case the UPS would likely not do any good and fail under the overload.

The biggest problem from such a load on your circuit is voltage drop in the line leading to your computer but the iMac's are speced to run with a line voltage all the way down to 100 volts. As i indicated earlier, if the voltage got that low I am sure you would see some other artifact such as the UPS tripping, the lights in your room being noticably dim etc.

Another thought that comes to mind is that perhaps you somehow have an IP address conflict between the miniMac and the iMac that is quitting. I run into that quite a bit with my Wife's computer as I have 6 machines in my office that are on for awhile and then off for awhile and from time to time turning on one of mine will cause hers to hang and invariable it is because somehow the router is assigning the same address to both machines.

Any other insights you can think of would be interesting to hear about.

C U

Jim

Fat Fingered from my iPad

Here's an update on my Mac.

I made the new user account ( which was a pain setting everything back up the way I like it) and the problem disappeared for a couple of days. BUT it came back! I haven't had a lot of time, due my in-laws health issues, so that was as far as I've gotten and have just been dealing with random screen shut offs.

Last night, the screen was shutting off right and left. So I had the inspiration to check to see if the LCD was still on and maybe the backlight was the problem. Turns out thats my problem.

To check this you need a fairly darkened room. Take a bright flashlight/torch and hold it by the darkened screen at approximately a 45 degree angle to the surface ( it might take a little fiddling with the angle to find what works for you). IF the LCD is still on, you should be able to see open programs or whatever you were running through the glass. I set up a browser window that had lots of white on it, like this site. Then I could command W to close the window and watch it happen to be sure I was seeing what I thought I was seeing.

So now I have to get it in again so this can be repaired. Which will be hard to do with a tight schedule.

Hope this helps.

Actually, now that I tried it again. Light that was perpendicular to the screen worked best.

Nice work and perhaps that will save the tech's some valuable (i.e., your $$) time.

Let us know what you find when it comes back from the service dept.

Jim

Excellent! Glad I could help!

I've got a Genius Bar appointment tomorrow at 12:15 CST. I'll report back what was said and/or done. I'm hoping for action but expect to have to leave the mac with them. I don't see how they could point to software as the culprit in this problem.

Apple has my Mac. They ordered a backlight kit for it and a LCD kit as well, just in case. They're going to run some tests to see if they can replicate the problem.

Here's their notes:

"Problem Description/Diagnosis

Issue: Customer states that unit is turning the backlight off intermittently, at lest happening a couple times a day, customer is having to press control shift eject then control shift like switching to external monitors and it will come back.

Steps to Reproduce: Could not duplicate at bar but has been in before for same issue,

Proposed Resolution: Run asd while waiting on part, see if backlight will go out in the asd os, if does replace backlight board. Loop in os until issue is verified,

Cosmetic Condition: No dents on edges, light dusting on stand and finger prints on LCD.

Known Liquid Damage: No

Check-in Required: Yes

Estimated Turn Around Time: We'll call you in 3 - 5 days

Mac OS Version: 10.7.4

Hard Drive Size: 1TB

Memory Size: 12 GB

iLife Version: Unknown"

We'll see...