Modding a proprietary HP SFF PSU, can i skip the 5V and 3.3V power in a 20-pin ATX connector?

[quintessence]

I have a few of these HP PSU's for SFF: https://www.cpumedics.com/hp-503376...for-hp-elite-8000-8100-8200-sff-pro-6000-sff/ and I'd like to try to run a mini- ITX board with 24-pin ATX (plus 4-pin) over it. Found a wiring diagram for doing the opposite (converting normal ATX PSU to power HP SFF Desktop): https://h30434.www3.hp.com/t5/image/serverpage/image-id/132482iDA0CF9FC14EB9826?v=1.0
SInce the PSU doesn't seem to have 5V or 3.3V rails, can I still power the mini-ITX board? I'll only be running a 2400G and maybe a SATA SSD.

 

[quintessence]

based on my research of PicoPSU's... i'm thinking i need the lower voltage rails and should get one of the aforementioned...

 

[Arboreal]

It looks like your HP PSUs are only delivering 12V, with the 3.3V and 5V supplies created on the motherboard. This is like on thin ITX boards that take either 12V or 19V and have onboard power distribution to sort that.
Yes, I would say a Pico PSU would replicate that function.

 

[LegionDD]

I've used numerous PicoPSUs to do exactly that.
I usually pair them with an inexpensive, passively cooled 12V PSU. The PicoPSU unit will take those 12V and generate all the other voltages a mainboard needs.
Wherever you need 12V you can just pass along the line from the 12V PSU (no need to run it through the PicoPSU first).
The PicoPSU itself has a plug for drives, supplying 12V, 5V and 3.3V to a SATA power plug.
This method really simplisfies cable management, as you've got only one 12V line to deal with for most things.

You just have to make sure your cables from 12V PSU to PicoPSU/System are thick enough to handle the power requirements.

 

[quintessence]

Got it working with a cheap PicoPSU from eBay! to power a Ryzen 2400G on a mini-ITX ASRock B450.
but dang is the PSU fan LOUD!!!! The stupid HP 503376 PSU fan is going full blast, it apparently has a FanCmd pin on the skinny connector where i jumped the PS-ON pin. The FanCmd pin takes a PWM signal. I have a PWM generator but it didn't help because I don't know what to output exactly. Saw another website that linked to some HP patents and design briefs that mentioned 25kHz signal among other things but I was unable to get the fan to slow down. I'll probably just rip out the fan because I don't think it will be necessary based on the configuration with no video card and a single SSD.

This build will be for a friend who I encouraged to DIY a case or let me 3D print one.