iMac randomly sleeping on its own

[Jamescunningham]

Hi everyone. I am new here. I have read many posts before posting myself. I have a late 2009 27” iMac running Sierra 10.12.6 3.06 ghz core 2 duo 4gb 1067 MHz ddr3 with 1tb memory. it just goes to sleep very randomly, sometimes within seconds of each other. The cpu stays running. I’ve read all kinds of fixes. Here’s WHAT I HAVE ALREADY DONE:
Reset PRAM
Reset scm
Checked log
Checked for dust
Checked for overheating
Adjusted screen brightness down
Turned on and off hot corners
Set monitor and cpu to never sleep.

Please help!

 

[mikehalloran]

Reset PRAM

Technically, you reset the NV RAM but it's the same thing.

Replace the NV RAM battery. The OE is a heat resistant BR2032 but the common CR2032 battery is fine.

I have a late 2009 27”

Here's the bad news. Unlike every other Intel iMac, that battery for the late 2009–2010 is on the back of the motherboard. Here in the Silicon Valley, most places charge $75 labor to replace it.

iFixIt has a page with instructions. If you decide to do it yourself, here's a tip. Get a bottle of white-out and mark the side of every one of those tiny in-line connectors so that you know which way they go back together. Unless you have really good eyesight and experience, this will make reassembly faster. If you get one wrong, you stand a good chance that the fan will roar full on when you are done.

If you still have an HDD in there, this is the perfect opportunity to install an SSD. It does not add 5 minutes to the job. All you need is the drive, a temp sensor (or short out the original if feeling lucky) and a $12 bracket (optional —double-stick foam tape works).