I have an old server (around 10-15 years old). Mobo, CPU and RAM are not great, especially now, but the chassis is pretty cool (server type, rack mounted with hot-swappable HDD trays).
I was planning on upgrading the PSU for one with a quieter fan and running it with older hardware until i feel like upgrading everything else.
The new PSU arrived a few days ago, the server did not boot, DIAG_CPU LED lit up. I assumed it's just the old thermal paste - sometimes CPUs overheat very quickly without it.
Today i replaced the thermal paste, tried booting but it still got stuck on the CPU. I followed by disconnecting all the peripherals one by one, removing second stick of RAM, yadda yadda. Eventually i ended up with mobo outside of the chassis, with nothing except 1 stick of RAM and CPU on it, plugged into the PSU and yet - nothing, DIAG_CPU.
As a sanity check i decided to plug in the original PSU and somehow, it booted up (well it went past DIAG_CPU and DIAG_DRAM. It got stuck on DIAG_HDD but there was no HDD plugged in so it makes sense).
At this point i did not know what to google so i just went with "old mobo sf 750 doesnt boot" and i was greeted with a single reddit thread. I haven't checked the standards but apparently either a newer revision of the ATX standard made one of the pins optional, or it just was unused for the past 10 years so manufacturers decided to omit it. Enough said that the PSU is lacking one specific pin (-12v to be exact) on the 24-pin connector and some older motherboards/CPUs needed it to work. I checked and indeed, my old PSU has the pin and new one does not.
To say i am shocked is an understatement. Out of all the connector standards in a computer, fucking ATX was the last one i would expect to be backwards incompatible. With full confidence i declare that i SHOULD be able to plug a modern new PSU fresh off the shelf into a 20 year old motherboard and it should fucking WORK. The connectors should be extended to accomodate new features, or perhaps you can make new standards of connectors altogether, but an ATX PSU should work with every ATX mobo, period.
I googled a bit more, and found two more sources that confirm this to be an issue. Not many sources but then again - it is a very specific scenario that not many people are likely to run into (10 year gap between mobo and PSU combo).
All in all it's also a bit funny and an excellent learning experience. All that does is make me get rid of old electrojunk and upgrade the server faster. It is not a big deal on paper but still - i am pretty mad. You can't just make PSUs that ignore years of compatibility.
The cherry on top is that the physical connector still fits - the pin is just missing. Unbelievable.
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