Testing power supply for working system
I've read a number of messages here about iMac power supplies, but they all seem to be about completely dead systems.
My mid-2010 27" imac powers up and boots, but it's performance is unreliable. It will boot very slowly, and trying to install an OS to it (El Capitan up through a Patched Catalina) will run for a time, but the install will eventually hang anywhere between 20-80% of the way through. Interestingly, the same failure happens with Fedora 39 and 40. I did get Mountain Lion (10.8) to install, but couldn't get it to upgrade to a newer version. Also had LMDE6 (Linux Mint) install but that eventually locked up after 3 hours, after which it would lock up within 5 minutes every time I restarted it.
It has new memory, SSD, I cleaned out the cooler fins and replaced the thermal paste. Currently I have been running it with the LCD removed (forcing it to display to an external monitor) so that I can have a fan blowing on the system boards. Running from a pre-installed Catalina (patched) disk it ran for 15-20 minutes and suddenly dropped power (and booting to a HDD on the SATA connector still took 15 minutes)
Long-winded explanation, but it leads to my question on the power supply. I have read that a failing power supply can cause some of these symptoms. The problem is, I don't want to throw more money at it trying to make wild guesses at what's wrong (the parts I've bought thus far can be used in various other machines). I would like a more determinate means of identifying or eliminating the PSU as the culprit (it could just as readily be the main board or the GPU).
As al alternative to replacing the PSU, is there some way to temporarily adapt an ATX power supply to power the iMac? I would think it would be a good way to test the rest of the system taking the iMac power supply out of the equation.
If nothing else I could do a monitor conversion, but I'd have to find extra-short cables to move the I/O ports to the back of the shell.
Update (05/09/24)
I'd need to pull the board to check the caps (would be a few days). I did upgrade the CPU, although the system was having it's issues with the original CPU. The RAM that was in it when I originally bought it was bad (it wouldn't boot, and the beep code indicated bad RAM). I had initially tried it with RAM from a couple of MacBook Pros I had upgraded (2010, 2012), then bought some Crucial 8G RAM. Again, same behavior before and after the RAM swap. Yes, it would be so much easier if it started failing after I swapped parts. Although I should check that the memory from the MBPs wasn't already aftermarket.
The SSD is a 1TB PNY SATA III (I had thought a SATA III drive merely would be limited to the SATA II speeds). Originally had a Western Digital WD1001FALS.
- Original CPU: Intel Core i5-760 (2.80GHz)
- Replaced with: Intel Core i7-870 (2.93GHz)
And I didn't mention that yes, all fans are working.
And I'm thinking that if I'd need to remove the boards to inspect them anyway, I could add an eSATA port on the back to connect to the extra SATA connector. Would be faster than USB2 or FireWire. Has anyone tried that before? Maybe this one from StarTech https://www.startech.com/en-us/cables/es...
Update (06/24/24)
From a suggestion elsewhere (a Mac-specific site) there was a suggestion to try reflowing the MXM video card, or replace it. Reflowing broke the video card completely, so eventually I tracked down an upgraded video card for the system. I had been sticking to parts that could be used elsewhere as well, figured I'd try just ONE specialized card (it's not Apple-specific, but I doubt I'd ever have anything else that uses MXM video).
Installed the card and tried powering the system on. No boot whatsoever. Unplugged the connector for the power button on the mainboard, jumpered the pins there, no power. Had swapped power cables & power strip port (that work on a monitor), no change. Removed the MXM card (it has previously booted without the card), no change.
I'm not going to start throwing more parts at it. If I don't see anything bad on the PSU or mainboard, I'll just pull out all the internals and do a monitor conversion (the resolution on the panel is better than any of the 27" screens I've seen at the local stores). The mainboard and PSU are already out of the system. I should probably pull out the backlight board and inspect that too. I'll just wait a while because right now this machine has p***ed me off too much, so let it sit a bit.
Had previously tried this machine with memory I pulled from a couple MacBooks (upgraded their memory with the OWC 16G upgrade), and the behavior was the same as with the aftermarket memory. The SSD's specs show it as properly compatible with SATA II
