imac will not start after shutdown

[Anim]

Hi all

I have an old 2007 24" iMac that has worked flawless for the last 10 years but in the last couple of months it has started to show this odd problem.

If I click the apple menu and shut down then once it is off, it will not start back up. I have to remove all cables, hold power for 5 seconds then reconnect everything. I have to repeat this twice. Then it will power up as normal. Additionally it will not wake from sleep either.

Opening her up, the LED's inside all light up when it starts so no reported hardware fault. The fans are all clear of dust and spin up as normal.

I have verified disk permissions and performed all updates.
I have done Option+Cmd+P+R

It seems to only happen with a soft-shutdown. I can restart the machine over and over without issue. It is just after you shutdown the power button will not start it back up unless I do the disconnection routine twice.

I will change the PRAM battery and see if that helps.

Any other ideas what can cause this?

Thanks
Anim

 

[Tim in Scottsdale]

Hello

Locate the power supply inside, and look for bulging electrolytic capacitors. These look like little cylinders, and the heat will degrade them over time, resulting in power issues.

 

[Anim]

Thanks. Will look at PSU after PRAM battery replacement. If it is the logic board will just bin it.