I then tried both power cords with the Core 2 Duo and it would not power up either. Thing is, I only unplugged from the Minis and not from the surge protector. So I swapped the power cords between the two minis and got the same non-response from the Core Solo. No chime, no power light, no sounds like the fan or hard drive spinning up and nothing on the monitor. I shut down again and tried to power up the Core Solo, but got no electrical response whatsoever. I think that is when I noticed that the power light on the Core Solo case was not lit. In this initial reboot, the Core 2 Duo restarted from its internal drive rather than the Core Solo, which had been configured as the startup drive. From my Power Mac days, I've always configured the clock to show the seconds so that I can differentiate between an application having problems versus the finder. What made me recognize this crash as different was that some of the digits in the menubar clock were not being displayed as well as that it was frozen. I didn't really pay attention to the Core Solo in target mode as other, largely Firefox-induced crashes, had been handled in this manner without necessarily having to reboot the target machine. Thinking back to when it happened, I powered down the Core 2 Duo with its power button, as it stacks on top. Any idea how to test and/or fix the fan I have? I have a digital multimeter available but am not too savvy with it beyond testing continuity and DC voltage. And also, the cost is as much or more than I paid for the Solo in the first place. Haven't seen too many options to replace it, except from China, which makes me wary. My best guess then is that the fan has failed. I finally opened up the Core Solo and pulled the hard drive which I have been able to access (and even boot from) via a Sabrent USB-DSC9-Hard Drive Converter, eliminating that issue.

It works with either power supply, eliminating that issue. Swapping power supplies seemed to kill the Core 2 Duo also, but after some time unplugged, it booted up again. I tried rebooting the Core Solo but all I got was dead air. I rebooted the Core 2 Duo but it booted into its first partition because the designated startup paritition wasn't found. That is until I tried to wake up from sleep about a week ago and the screen was frozen. Lately they had seemed a bit noisier, but no where near the howl of the G4, so I found it negligible. I've even used one of its partitions as the startup disk as it had the larger hard drive and I already had it configured as desired. Anyway, I've been using both Minis together with the Solo mounted in target disk mode. Last year I was contemplating a processor upgrade but settled for picking up a Mac Mini Core 2 Duo for $55 and avoid the risk of botching the upgrade. I picked up this Mac Mini Core Solo for $20 plus $15 for a monitor adapter in 2019 when the power supply in my MDD G4 failed and I wasn't able to come up with a fix.

How to test mac mini power supply