Is my iMac Power Supply failing? (Or External SSD issue?)

[mrbobdobolina]

Situation: 27" iMac (2017) started to feel slow, DriveDX tells me that the internal HD is starting to fail.
Contemplated options, bought a 2TB SSD, installed the OS onto it, put it in a case, and got a Thunderbolt 3 to USB 3 adapter cable. Booted from this drive, migrated files over, everything runs great. (Debated opening the machine to put the SSD inside, didn't want to if I didn't need to... at least not yet.)

1 month later: This morning the iMac was off. It didn't want to boot. Unplug, hold power button for 10 seconds, plug in, boots fine. An hour later the machine powers off while my wife is typing up an email.
During the reboot, the machine powers off. Each time it shuts down it won't reboot until I pull the plug (or turn off the power strip), hold the power button for a few seconds, then plug back in.

I've plugged into an extension cord to eliminate the power strip. Unplugged extra monitor, Nuphy Keyboard, Printer USBs.

I can still boot from the internal drive. The last couple times I've done that I get an error saying that the external drive is unreadable. When I unplug and replug the drive, it shows up normally. And I have been able to boot off the external drive as well, but when I come back later the machine is off...

This morning I was thinking it was the power supply, but as I type this I'm thinking it's an issue with the SSD losing connection... I have now confirmed that booting from the internal drive it also just shut off without warning. It isn't consistent. What should my next troubleshooting steps be?

(If it does end up being a power supply issue, I plan to install the SSD while I have the machine open.)

 

[Chuckeee]

It certainly sounds like a PSU issue, although in my experience (I have had 2 iMac that had PSU failures) they happened after a bit more time (10-11 years).

 

[gilby101]

Since you are not confident of your diagnosis you could end up replacing lots of bits before getting anywhere. Take it to a local Mac repairer to get the fault(s) diagnosed properly. Might well end up being time for a new Mac rather than repair.

 

[Fishrrman]

Agree with both replies above re the power supply issue.

I would check ifixit.com to see if they have a tutorial as to what's involved in changing the power supply... but...

...Also agree that it may not be worth putting a lot of money into at 7 years old.

 

[mrbobdobolina]

Thanks everyone for the responses and advice.

I don't use the iMac a lot anymore, I've upgraded to a Mac Studio for my main work, but the machine is powerful enough I'm not quite ready to give up on it yet as a secondary workstation. I went ahead and ordered a power supply unit and I'll see how tough it is to take this thing apart. (I've done repair on older iMacs with magnetic screens, never ones where the screen is adhered on.) I'll install the SSD internally while I'm at it. And hopefully give this machine a little bit more life. (And if something goes horribly wrong, it won't be a complete disaster.)