Help with SMC

Poncho

macrumors 6502
Original poster
Jun 15, 2007
347
144
Holland
As of a week ago, my iMac will either shut itself off when asleep or, if closed down properly, will not start up when I press the power button the back.

This behaviour is intermittent.

It will start up if I reset the SMC by taking the power cord out, wait 15 secs then plug it back in.

So does anybody have any idea why the SMC needs frequently re-setting, but not always.

Happens if the Mac is attached to a power strip more often than not. Seems OK when plugged directly into a wall but only have one plug socket so can't use it like this because I run a dual-monitor set-up and some external hard drives though it happens when plugged into two different power strips and when everything else is disconnected. I have also tried two different power cords that are known to be good and no difference either.

Is it because I might need to replace the battery in the 2008 iMac I have as this might remember the SMC settings and now isn't?

I downloaded and ran Apple System hardware test software by booting from a thumb drive and it said all was OK.

Anything else I can check or ideas for troubleshooting? Can't afford a new Mac:(
 

tjwilliams25

macrumors 6502
Aug 10, 2014
316
60
Montana
This happened to me a few years ago. I had a short in the wall that was causing the power to fluctuate and it would trip the internal circuit breaker of the iMac, and you have to reset it the same way as the SMC. I just had to move it to a different circuit in my house until we could fix it.
 

Poncho

macrumors 6502
Original poster
Jun 15, 2007
347
144
Holland
Ah! Now that's interesting! I shall put the Mac on a long cable and plug it into another power socket and see what happens. Thanks for the info!
 

Poncho

macrumors 6502
Original poster
Jun 15, 2007
347
144
Holland
you might want to consider getting an UPS (uninterruptible power supply)
Thanks for the advice, and it's good advice but I was actually running the Mac on a UPS when the problem first occurred. It was an APC ES 700. So I thought that was faulty. But tests with other devices run from that show that it isn't. For the meantime have set the Mac to never sleep in System Preferences/Energy Saver and this stops the problem from occurring,
 

chscag

macrumors 68040
Feb 17, 2008
3,193
986
Fort Worth, Texas
For the meantime have set the Mac to never sleep in System Preferences/Energy Saver and this stops the problem from occurring,
As stated above, you probably need to replace the PRAM battery. A typical PRAM battery is supposed to be good for 10 years but a lot depends on how often you turn your iMac off and then on again.
 

Tech198

macrumors G5
Mar 21, 2011
13,944
1,636
Australia, Perth
If your asking why the SMC need more frequent resets, I have no idea.... It is software, the same as BIOS software/hardware on a PC, but i've always found yes the SMC and/or PRAM does need more frequent resets...

Apple says "It's software, so like anything else, gets corrupted" which is true, but doesn't answer the question..

For example, i've never had to reset any settings back to default on PC's as much as I need to do a SMC reset on Mac.

Most likely the SMC and PRAM contents controls allot more software configuration and that would be the reason why its more troublesome. On one hand it may make sense, but if u ask me.... no wonder u need to reset it more,