It's black magic, right? The buck converter "simply" creates a potential difference between the input and output pin with the output voltage being below the input voltage. If it can reduce a +24V input by 17V to make a +7V output, it can reduce a +5V input by the same 17V to get -12V out depending on what you consider a ground reference. It's all a matter of perspective, like the guy in the video explained.

I know the built-in pot is not great but it's good enough for my application. The -12V aren't actually used anywhere, they just need to be present for the PSU controller...

It's a bit of an open secret that you can operate a buck converter as an inverter just by reversing its polarity. It's NOT a common ground, at least not with the rest of the system, that's the key. The only thing to look out for is the maximum voltage rating because it applies to the total potential difference from +5V to -12V (i.e. 17V), so a buck converter rated for 18V is just sufficient, but it won't work on +12V to generate -12V because that's 24V difference....

Of course the best way would be to replace the original blown IC on the original PCB, but that's a huge effort. The easy "permanent" fix would be to connect the $3 buck converter board internally to 5V and inject the -12V output into the respective rail (also internally). It's pretty much exactly how this rail is originally generated, just using a separate little buck converter board instead of the onboard one. For my use case it's perfectly fine and the PSU is even still ATX compliant with a functioning -12V rail. I think it's a very niche case where this particular rail gets blown,...

I've already put the PSU back together for testing, so here's a picture of the insides from the internet and I marked the buck converter used for -12V:
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It's very compact and a full inspection would require extremely tedious desoldering of the vertical daughterboards, which...

A few drops of watercooling liquid were spilled on it and apparently some made their way in. The PSU worked for a day, then it stopped and is now in the permanent protection state with missing (only) the -12V rail. I took it apart, cleaned all liquid stains I could find and checked for broken components, but nothing looks damaged on the surface. I assume the -12V buck converter blew due to over current, that's all. The rest of the PSU works, all voltages are present, it just won't stay on with missing -12V......

I have a Corsair SF450 SFX power supply with slight water damage. 5VSB is present and it turns on via the ATX PS_ON pin, but immediately goes into protection mode (relais clicks on and off). During the brief moment before protection kicks in, all power rails are present except the -12V rail, which also went low resistance (24 ohm). I don't know if protection mode is triggered by over current on -12V due to the low resistance (the current limit is only 0.36A on that rail according to spec) or simply because the voltage is not present. I removed the IC generating the -12V (54231 buck converter)...

I found a DDR4 datasheet and checked all voltages (most are parallel but not all) and they're all good. There was a tiny bit of corrosion in various places (as mentioned before) which I've cleaned. The CPU hasn't been removed until the RAM problem and the socket pins look completely pristine, no corrosion, no bends, no foreign ojects. I checked everything for physical damage but nothing stands out. The actual RAM sticks and CPU are good (tested in another mainboard). I think the only chance to find it is a RAM tester board, but at this point I found a cheap Asus Z170i as a perfect replacement...

Hi!

I have an Asus Z270i mini-ITX board with a dead DIMM slot (the one further from the CPU). The board POSTs with only the other DIMM populated but gets stuck with the DRAM error LED when the bad slot is populated. The test RAM and CPU are known working (confirmed in a different board, both memory channels are fine). The board was working for many years in a watercooled system and had a tiny bit of corrosion in different places (which came off without issues) and no visible component or trace damage.

What are the steps for DIMM (DDR4) socket troubleshooting? Since the...

Very helpful board for the little man to fight against the tyranny of our BOFHs, one password reset at a time.