Model A1174 with 2 GHz Core Duo or Model A1207 with 2.16 or 2.33 GHz Core 2 Duo

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Monitor going black on my iMac?

After about 15 minutes after I turned the computer on the screen goes black. When I press Opt, Control, Eject and then the space bar it comes back on. It will continue this process many times (at least 9 or 10). When to screen get a little dim then it works fine until the next time which could be anytime.

I've read all the answers and I'm reading it could be anything from a converter cable, logic board, monitor and graphics card.

I've tried resetting the SMC and PRAM...didn't work.

If anyone has been able to correct this problem I would love to know how otherwise I might be looking at a new computer.

Thanks

Peter

Answered! View the answer I have this problem too

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Try lowering the brightness to a very low setting does it appear to take longer for the display to go black? Also have you tried an external monitor to see if there is any difference?

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I tried what you suggested about lowering the brightness and it seems to be working.

I haven't responded sooner because I wanted to test it before I said anything.

I lower the brightness about 25%. Then I tried raising the brightness a little and it didn't work. The screen started to go black.

So the 25% setting seems to be working. That was a great idea.

Why do you think it's working by lowering the brightness?

I hope it continues to work....I'll let you know if it doesn't.

Thanks for the suggestion.

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This was a diagnostic trick to isolate out the cause of the screen going out. Your problem is within the display it's self. The thermo sensor on the display panel is either going bad or the display it's self is over heating.

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First thing I would do here is make sure the vents on both the top and bottom of the system are free and clear of and papers or other objects.

Next I would get a vacuum out and clean the vents (top & bottom) of any dust build up. You may need to use a brush to dislodge anything.

If you find there was nothing blocking the venting externally then you'll need to go deeper.

Download from the App store or other source a temperature monitoring app. Monitor the temps from the display & CPU/GPU's. What is getting hot? Before and when you raise the brightness just before the display goes black.

Are you up to opening your system? Do you have the correct tools and an ESD mat and wrist strap? If you are up to it continue. If not it's time to get your system in to an Apple Store or an authorized Apple service center for deep cleaning and possible repair.

Review the iFixIt guide and open the system up using a soft brush and compressed air (canned air) blow out the dust and clean the heat sink grills of the CPU & GPU. Do not use a vacuum here!

If the system was not dusty and the display was overheating, you'll need to open it up to check the sensor and may need to replace it or the display.

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A friend of mine said it might be thermal grease that may be drying up and is relatively easy to fix. What do you think about that suggestion?

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Not in this case. That fact the brightness level gave you a different reaction (low Vs high). Points to a heat dissipation or display issue, not CPU/GPU inability to move the heat to the heat sink.

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As to it being an easy fix. Not really here, review the iFixIt guide. It's more work than what I had recommended you focus on.

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Check the energy saver in the settings. This was set to 12 mins by default in my IMAC. It can be set to increments of 3 mins or to a setting of "Never".

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Peter will be eternally grateful.
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