odd PSU behavior, CX600

[cicada]

I recently picked up a new mobo and a pair of Corsair CX600's so I could pull the cards out of my file server, where they were baking the crap out of my drives.  I've got the new system running with one 6870 on the first CX600, but I'm having some odd behavior with the second, which will be powering a pair of 5830s.

When I jumper the PSU (green PWR_ON to black ground) and turn everything on, it spins up and all seems well, but after about 30 seconds or so the PSU just shuts off.  

My initial thought was that it required some 3.3V or 5V load in order to stay up, however this is where it gets weird - if I jumper the PSU and power it up with nothing connected, it stays on indefinitely without any problem..

I've got several other Corsair PSUs - HX650, HX750s and CX430s, and all of them work just fine jumpered.  Architecturally, this CX600 should be near identical to the CX430, so I'm a little stumped why it'd behave differently.  I haven't yet tried swapping it with the working CX600, will be doing so in the morning, I'm just wondering if anyone has seen this kind of behavior with a jumpered PSU before?

[edit] These are the CX600 V2's, 80+ and 480W rated on the 12V rail.

[Yanz]

I have a cooler master gx550 and it does that too

[stryker]

my no name 850 watt did that. Originally I shorted its green wire to a back ground.  The psu would spin up but when I started the system psu up the 850 watt would shut down.

I resolved this by linking the 850 watt psu green wire to the green wire on the system psu so it all starts up together now and runs fine.

HTH

[cicada]

Well now that I know the CX600 is a group-regulated PSU, this makes more sense.

When the system tried to bring up the cards it was only loading the 12V rail, without 5V/3.3V load the PSU was shutting down as a protective measure.

I got it working fine by using a 100 Ohm resistor between +5V and a neighboring ground on the 24pin connector.  The same could be achieved by connecting a spare HDD or optical drive, or anything else that completes the 5V circuit.

When I was powering it on with nothing connected, the lack of load on any rail meant there was still a balance, and it didn't trip the current/voltage protection circuit.