Home built windows machine that has been running strong for years. Enclose is a Fractal R4 and it has 3 installed case fans currently. 2 in front and one in back. There is a little 5v/7v/12v switch on the front of the case to control the case fan speeds. I’ve had a few instances where changing this speed, usually from 12v to 7v causes the PC to reboot. The fans aren’t plugged into the motherboard, they go straight to the PSU. This happens more when I’m running something that is taxing the system a bit. I haven’t been able to reproduce it yet, but I’ve had the same issue of a sudden reboot when turning off my speakers, a self powered set of M-Audio AV-40’s, so their only connection is a 1/8th jack into my onboard sound.

I’m running a slightly overclocked old i7 4770k, a EVGA 3070, 2 physical drives and one SATA SSD. CPU has a basic aftermarket single fan cooler and then just the 3 case fans. PSU is a modular seasonic 750w which last I checked, should be producing a few 100 watts over what I need, it barely even gets warm and while it has a fan, it hardly ever turns it on so it doesn’t appear the PSU is being overly taxed. It’s old, maybe 10 years on this motherboard/CPU/PSU combo and I’ve never had an issue, but it could be slowly failing somewhere at this age.

The fan speed switch causing a reboot makes me think PSU, but turning it down from 12 to 7v seems an odd reason for a reboot as I’m drawing less power. The speakers shutoff reboot make me wonder if there is some static buildup or something somewhere that’s causing the motherboard to reboot. My Bios will give me a start up warning if a PSU issue caused a reboot, as it’s happened from power outages, and I’ve not gotten this warning any of the times this has happened. Motherboard is an Asus ROG Swift something, it’s not a bargain no-name, but it’s as old as the rest of the components. Only the 3070 is new and it’s been installed and running for well over a year now with zero issues.

Any ideas to troubleshoot? I’m planning to do a CPU/mobo/ram/SSD upgrade soon, and was planning on keeping the same PSU but wondering if that could be the culprit.