2008 iMac won't power up after power off

[Dennis Paul Eldridge]

Hi all, this is a new one on me...

I have an old 2008 vintage iMac, which I've repurposed using Ubuntu. It does have a bit of a boot issue though. It seems that, if it's been turned on and then powered off, it won't reboot unless you unplug it from the mains for a while. I would guess that something in the power supply needs discharging perhaps.

This is rather annoying, so if anyone out there could offer some ideas that would be great.

Cheers,

Dennis

 

[USB3foriMac]

So you plug-in the cord and it starts booting? Or you plug-in, then press the power-on button and it starts?
Could your power button simply be spoilt? This happens frequently.

Unplugging it for 15 seconds or longer resets the SMC. https://support.apple.com/en-us/HT201295
So you may have some issue there. It could be that your power supply capacitors are degraded. You could check by opening and visually inspecting the capacitors for deformation. Typically, the top of one or more capacitors could be bulged, or the bottom comes off.
It could also be some other problem.

 

[Dennis Paul Eldridge]

Yes, I actually did consider that the power supply caps may be in bad shape, so I'll check those.

The unit itself looks like it got run over by an eighteen wheeler - the front glass is missing, and the previous owner sought to festoon it with stickers. Also, the screen has some odd issues at the corners, but nothing that impedes the readability of the screen. Now that I've found that Ubuntu can revive this thing and make it usable I'll endeavour to fix it up.

Cheers

 

[USB3foriMac]

Since it's this old, you might also want to check or replace the button battery on the logic board. You might want to do a search whether a depleted battery can cause your symptoms.
Can you get back on the question about how the unit starts up, power button or not? It is quite common that the power button is spoilt. In that case, use a flat screwdriver on the contacts while holding the screen creating a gap for your hand to get in. That way you can test whether the button is the culprit. Be careful not to cause any other short circuit. Isolate the shaft of the screwdriver with tape.