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

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...

I picked up my iMac today from Apple. They replaced the LED backlight boards. I've been using it non-stop tonight (about 6 hours straight) and have not experienced any problems. Everything on the Mac is how it was, the drive was not erased for a Lion reinstall. So far so good. If it starts acting up, I'll post another update.

Hey guys(and/or gals =P),

I just stumbled on this thread after digging up my 07 iMac that I've had packed up since it "died" on me 4 months ago.  I am a gamer and was playing the new Diablo 3 game that just came out when I started having a similar problem.  jjhaffner, glad to hear that you resolved your issues with yours.

I'm getting ready to do the flashlight test(I'm waiting for my display to turn off) and I had a question if anyone had a second monitor hooked up to his/her computer while the display was turning off?  I wondered if a second monitor might remain on if it was a display issue, but to no avail, the external shuts off along with the main display.

I feel foolish right now also because I took it in to get diagnosed and repaired, and the tech said it was a logic board issue which would be a $1,200 fix, all of which would be chargeable to me due to my lack of continuing apple care.  He then recommended that I just try and get some money out of it by selling it as an "as is" computer on ebay for spare parts.  With that recomendation he offered to wipe the computer for an additional fee which, regretably (now that I have another idea to try), I accepted.

The shift+ctrl+eject hotkey doesn't work to bring my display back on, but I'm wondering if that's the case because I don't have any OS on it yet.  I'm waiting for a friend to lend me his Install Disk to get it booted back up.  Hopefully I can run the full setup fast enough before the screen dies on me.  Or maybe I can just use a flashlight =).  That'd be fun.

I'll update you what happens, but my big question is, did anybody try using an external monitor through this process and what did it do while the screen blacked out?

So I tried the flashlight test and I couldn't see anything, it was pitch black.  Am I missing what I should be looking for or is it tough luck?  What tips do you have to spot the picture w/out backlight?