Model A1311 / Mid 2010 / 3.06 & 3.2 GHz Core i3 or 3.6 GHz Core i5 Processor

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iMac goes to sleep mode even while using it

After installing mavericks my imac keeps on going to sleep mode approximately every 25 seconds. However, this issue occurs only when I turn it on from a complete shut down or when the power cord was detached. When the issue happens, I simply RESTART the machine at the issue is gone. It does not sleep anymore but after using it for a long period, it freezes. The mouse pointer works but no response from anything on the window. I would have to restart the machine again by pressing and holding the power button. Tried to reset SMC etc but no go. I set my imac to never go to sleep and display sleep at 15 mins. I tried to dual boot with mountain lion and issue is even worse when booting with mountain lion. All of these happened after installing mavericks. I never had this issue with mountain lion before. The temp is no greater than 50 degrees Celsius. It is an intel i3 imac. Please help. Sorry for my english I'm from the philippines.

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Hopefully you and your family are OK from typhoon Haiyan. Our prayers go out to all that were effected by the super storm.

As to your iMac problem. Try lowering the brightness to as low as you can and still use your system does it work better then? Also do you have an external display which you can connect? If you do does it go out with the main display?

Depending on what you find you could also run Apple's Hardware Test AHT and see what error code you get. Also you could try running a temperature/fan monitoring app to see what it reports.

I suspect the thermal sensor on the LCD is failing and/or you have some dirt buildup which is blocking the systems cooling.

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Thanks for the concern and thank God we are not much affected by Typhoon Haiyan. It's truly heart-breaking to see the condition of the people in Tacloban City Philippines. suffering physically and emotionally from shortages in food, water and shelter. We are very thankful from all the aid coming from the different nations around the world including the USA.

As for my iMac, i tried lowering the brightness to it’s lowest level but same issue occurs. I don’t have an external display to check if it also goes out with the main display but i’m sure, whenever the display goes out, it’s under sleep mode because the fans stop working and the mouse light turns off. it takes long to wake up and i have to press anything on the wireless keyboard just to wake it up.

As for the Apple Hardware Test, I would have to buy a USB keyboard coz i read somewhere that i need to use a USB keyboard to perform it. I can’t seem to enter AHT using apple wireless keyboard (Pressing and holding D key while turning the iMac on)

I installed SMCFan Control and increased the fan speed and temp right now in 42 degrees Celsius but the issue still occurs.

Its just so curious why the issue would only happen whenever I unplug my iMac. After I restart it the issue goes away but for a long period of use the machine freezes. the issue will also occur when the iMac wakes from sleep mode.

To verify wether this is an issue with the thermal sensor or some software glitch with mavericks, i have to get a USB keyboard to do the AHT. Thanks much..

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Happy to hear your family is safe.

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I'm not a lover of FanControl, it tends to mask underlying problems when used. I think the external monitor will be a good test to see what happens when it is connected. Yes, AHT does need a USB keyboard (any will do) you don't need an Apple keyboard. You could try resetting the SMC to make sure it's not messed up Intel-based Macs: Resetting the System Management Controller (SMC). Don't think you have a Mavericks glitch here.

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