2 Power supply units died after SSD upgrade

Hi all,

I have been in the process of upgrading some half dozen production machines in my office. The info and experience on this site has been an incredible resource.

Primarily we are swapping out HDDs for SSD’s. They are all iMac mid-2011, 27”, mostly i5 machines and most of the upgrades went smoothly.

To cure the fan sensor issue I have been clipping the 1 and 4 wires on the SATA cable and connecting the wires and sealing off the other ends at the plug. I have one i7 that is a 3.4 GHz that has been giving me problems. It was working fine, but showing signs of a dying HDD.

We opened it up and swapped out the old dying HDD for the new SSD. When we went to restart nothing happened. The LEDs showed #1 illuminated. We checked the test points on #1 and #4 and had no voltage. We then checked on #1 and 11 and there was 12V, which is the opposite of what we expected.

As we did some tests, LED #1 then blinked on when power was connected and then went off when we tried to restart. Then we only got a single blink upon power. It seemed like our diagnostics were changing as we checked. Then we had nothing. We suspected the power supply, but info we found also pointed to logic board and/or possibly video card.

Our local mac repair/reseller had a similar model with the same power supply and we purchased it to test, figuring it was the quickest way back to a working machine.

We put everything back together and installed High Sierra without a problem. Everything was working as expected. We shut down and moved the machine to another area of the office and booted back up. We heard the chime, the boot started, and then it went dark.

I haven’t been able to open up the machine to view the LEDs yet, but it seems like the power supply failed. That seems like what we had just seen.

Can you think of anything that would have caused a power supply failure, twice? The machine had been fine before, but was showing signs of a failing HDD. All the other upgrades have gone without a hitch. Hope you all have some experience that can help. I will be able to open it back up shortly.