Seasonic SS-850KM Power Supply won't turn on with a jumper, but turns on when using an empty motherboard. Am I missing something?

[Siapa hayoo]

I have a Seasonic SS-850KM Active PFC F3 Power Supply and I want to use it with an eGPU, so its not going to be connected to a motherboard and I thought I would just be able to turn it on using the PS_ON jumper/paperclip trick, but it just won't turn on. The fans would spin for like 1 second and everything would turn off again, I also think I hear a relay clicking? But then I got an old empty motherboard and plugged in the 24pin to it and using the power button pins it would turn on just fine.

 

I don't really know what I'm missing here, I even bought a jumper plug that is just a 24pin slot with the jumper wire and it still doesn't work. I'm pretty sure I have done this before on a different power supply and it worked just fine.

 

It's also not just on some mode where the fans are disabled, I checked with a multimeter and there is no voltage.

 

This might have something to do with it, but I don't really understand what I need to do. Something to do with sense lines? https://electronics.stackexchange.com/questions/97306/does-an-atx-psus-ps-on-signal-require-resistance

[191x7]

Maybe it needs some load?

[Siapa hayoo]

I have the eGPU plugged into it and its still not working.

[mariushm]

The sense wires are on the pins which have 2 written on them : 

Basically, a wire (for each voltage) goes from the 24 pin connector back to the power supply and gives the power supply the actual voltage measured at the motherboard connector. 

If there's some voltage drop on the cable going to motherboard, the psu can counter that by increasing the voltage on that rail slightly (ex send 5.1v through the cable, so that 5v reaches the actual connector and 0.1v are lost on the wires between motherboard and power supply)

It shouldn't matter that the 24 pin connector isn't plugged into the motherboard , but the power supply may turn off if there's no actual consumer drawing power from the connector. Maybe you could work around that by connecting a fan to ground and 12v in the 24 pin connector, or maybe some led strips or maybe an incandescent light bulb (cheap, see motorbike bulbs, 30-60w signal lights for cars etc etc, and car parts place will have them)

 

Maybe you're also tricked by the power supply if it has hybrid mode / fully passive fan - it may turn off fan if there's not enough power draw.

 

 

[Siapa hayoo]

So if the sense wires are just checking the voltage at the end of the wire that means that shouldn't cause the PSU to not turn on right? 

 

I have the eGPU (GPU+Adapter board) connected to the power supply GPU/PCI-E connector, so there should be a load there. But there is no load through the 24 pin connector, is that the problem? Also, using the empty motherboard I can turn it on without any other load connected.

Edit: I also have a bunch resistors that I could use to load the PSU but I'm not too sure what values I should use

 

Also, I have checked with a multimeter and there is no voltage, so its not just the fan that is off.