Model A1312 / Mid 2010 / 3.2 GHz Core i3 or 2.8 & 3.6 GHz Core i5 or 2.93 GHz Core i7

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Monitor shuts off but computer still running

Sometimes with no apparent correlation with internal hardware temperature my iMac screen shuts off, but the computer itself still running (I can type something, use it...as usual, but the monitor is off. I can see my desktop if I point it to direct sun light).

I've tried to restore the original configuration but it's the same.

There is not an exact delay time before shuts off; it can happends some minutes after startup, some hours later or some weeks later.

To restore it I need to put it in stop (with the power button) then press it again to awake it. It turn on again without any problem.

iMac 27 Mid 2010-Intel i3 3.2-2GB DDR3 Ram, OSX10.8.2,ATI Radeon HD 5670 512 MB.

Any idea?

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I've tried with PRAM reset (5 times) but nothing is changed. After a day the problem is here again. I've turned my iMac in sleep and resumed it.

At Genius bar a technician said to me:

A) it could be a problem the power cable of the monitor (about 100€)

B) ... or with the graphics card (about 200€)

C) ... or with monitor itself (about 300€)

I really don't know what I should do to repair it. This strange problems does not happends every time...it's random... and it's the same since months...

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Hi Dan, I'm sorry to tell you the only way to get this fixed is by ringing Apple, even if your mac doesn't have a warranty. It is a real frustrating thing, you think maybe is fixable, but it's not. I have repaired computers for some time and i stopped it happening for a week, but then it went back. Apple replace me logic board first, but it still didn't fix it, Apple then replaced the graphics card and the screen and that has stopped it doing it. So contact Apple, tell them even an windows computer would last longer yeah right. And you didn't pay $3000 to have this happen 5 years down the track, be nice and good luck. All the best

If they don't fix it, is an expensive job to replace the 27" screen.

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Mine was doing this. I removed all the dust inside the computer, especially around the RAM slot, where it appears to take in fresh air. There was a lot of dust. Then I installed Mac fan control. Between those two actions, it has not shut down since, about 4 month and running.

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Your LCD backlight is on the way out. You could either connect to an external monitor or get/do a LCD replacement.

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it is not this. i had replace this and charge me and the problem persisted.

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I just read this: The cause is heat. The SMC fan is not cooling down the system which is then shutting down because of the heat.

There is a temperature sensor in the drive to supposedly prevent this. However, if you've changed your drive like I did, and replaced it with a drive that did not have a temperature sensor, thent he fan controll gets all confused, doesn't turn on properly, everything heats up and then shuts down.

This also happens on factory installed drives when the temperature sensor goes bust. A lot of Apple's early drives for iMacs and MacBooks were really cheap and the sensor failed. I had to replace my factory isntalled drive because it failed. (Thank you time machine).

The solution is a simple FREE software download called SMCfancontroller that turns your fan on at specific RPMs, and turns it off when you aren't overheating. I installed the software and haven't had a "go to black" moment since. The software can be downloaded here: http://www.macupdate.com/app/mac/23049/s...

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The fan is fine, yes it looks like it's getting hot in there at times around 50c, you can download Macs fan controls cooling won't bring back the screen from cutting out. It it was overheating the whole computer would shut down, these computers are still operating in the background.

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Please reset PRAM 5 times by keep pressing Command, Option, P, R hearing 5 chimes except the first regular one. That will resolve the issue. If not, come back here and let us know. We will try to resolve it.

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i will try this and post my results

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I tried but still not working. Extranal screen is working but main display is not coming

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Tried this but did not hear any chime or any other reaction. What to you think of the fan control option?

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Ring Apple, and get them to pay for a new screen and graphic card like they did for me. The only way.

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try reset PRAM 5 times and problem resolve

but after few hours screen black again

any idea?

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My MacBook never had this problem until I replaced the magsafe adapter with an non-Apple charger (the Ostrich Replacement Macbook Charger 60w Magsafe L-Tip Power Adapter Charger) during the heat of summer. Whenever I was working the CPU heavily while the ambient air temperature was hot (20-25C or so), first the monitor would repeatedly shut off, and soon the entire machine would spontaneously shut down completely. The computer felt quite hot, so at first my solution was to shut it down for 20 or more minutes to let it cool off. But whenever I used the MacBook for long periods of time in hot temperatures, even this proved to be only a temporary solution. Ultimately, I ended resting the machine on top of a medical cold pack just to keep it running for an hour or less at a time. I then tried three of the solutions mentioned in this thread.

First, I tried resetting the PRAM, but this had no effect at all, as far as I could tell.

Second, I followed @jurgenkoppen's suggestion and downloaded smcFanControl, but unfortunately it didn't help nearly enough. I then switched to a different fan controller, MacsFanControl (https://www.crystalidea.com/macs-fan-con...), which worked much better. It's slightly more complicated to use than smcFanControl, but not by much; I set it to display the temperature of the CPU Diode, which consistently ran very hot very quickly, and I set the exhaust fan to run on auto. These steps immediately began to cool down the whole computer, and maintained a relatively lower temperature.

Third, after reading that a faulty power adapter could be responsible, and realizing that I had just recently replaced mine, I tried removing the power adapter and running off the battery. The result was striking: whenever the power adapter was in use, the temperature would climb VERY high fairly quickly, but when the battery was in use, the temp would drop to significantly cooler levels.

My MacBook still runs too hot when I work it hard, probably because of faulty hardware, but it doesn't shut down anymore after I made these changes.

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dan will be eternally grateful.
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