As mentioned in the article about updating bios, I have a PC built around a B850M motherboard. Two days ago, it just decided to stop working. When I pressed the power button, the fans would start to spin up, a red status LED would flash once on the motherboard, and then everything would go dark, all within less than a second. The one thing that remained on was the LED behind the power button of the case. The only way to turn the PC off was to turn off the power supply.

It was a sad moment for me because I only just built my PC less than a year ago on October 24th, and I expected my entire setup to last for at least two years before any parts started to give in. I guess I might have been naive.

Anyways, I got do diagnosing the issue on the same day, and looked up ways to test my PSU. A tutorial on YouTube showed me how to check if my PSU at least starts up. It showed me how to short 2 pins (out of the 24 that ATX has), and see if the fans start up. Mine did. And then I remembered that my family still keeps a multimeter around so I broke that out, and which the help of my brother, tested the pins one by one. Rookie mistakes aside, we eventually managed to get things set up and sure enough, every non-GND pin was reporting the correct voltage. So that made me think that my PSU was fine. At that point, it was a bit worrying because if the PSU was alright, then it’s either the CPU, motherboard, or RAM that is down; all of which were expensive to replace. But my brother pointed out that we could just try to wire everything up again and see if my PC booted. And magically it did. I was so happy I didn’t think to try it twice, and just packed up and went to sleep.

However, the very next morning the PC refused to boot again, exhibiting the exact same symptoms as before. This time I tore apart the entire PC, and isolated out just the motherboard (on a non-conductive surface) with only the CPU and one stick of RAM plugged in. I even tried resetting the CMOS values to factory default. Nothing worked. It was then that I decided to bring those three minimal components to the local repair shops and see what they could do to diagnose this further.

At the repair shop, the technician wired up everything I brought and thankfully the exact issue was reproduced immediately. After thinking for a bit, he thought out loud that the issue may be with the motherboard. But before he tried swapping out the motherboard, he tried on his own PSU first to see if that fixed anything, since it was a much easier swap to do. And amazingly, that was it.

As it turns out, even when a PSU works pin by pin, it may not work when put into a PC. This might be due to other variables like the stability of the current it provides. Please note that I have limited background in eletronic circuits so that’s nothing more than layman conjecture.

Since then I replaced my PSU and I’m now typing out this blog post of my repaired PC.

Now, for technical stuff that might be helpful to future me (or you, who’s reading this article). I have the Arctic P12 Pro PST case fans, and through some testing and tuning with Fan Control, I have found that at these fans operating at 17% of their full capacity is quiet enough such that I effectively cannot hear it.

The CPU cooler is the Thermalright Peerless Assassin 140. I’ve found that when these fans operate at 80%, again I effectively can’t hear them from outside the case, which is where my head is (usually).

So that’s how I set the baseline configuration (for when my PC is idle). Also, it’s worth pointing out that the BIOS of my B850M motherboard has the option to apply a setting to all fans, so you don’t need to configure one fan curve at a time.

Cheers, and until next time.