Help identifying a computer PSU - non-standard HP molex?


I was thinking of re-purposing an old HP/Compaq desktop PSU for use on a project that needs 12V, but I'm having trouble getting the PSU to start up. I've used ATX supplies before, and have therefore had to short the POWER_ON connection to get them to start, but this unit seems different.

For starters, instead of a 20- or 24-pin Molex, this one has a 10-pin and an 8-pin Molex.

So connector one looks straight forward enough - a bunch of grounds, a pair of 5v red and a pair of 12v yellow:

    red black black yellow
    red black black yellow

Connector two looks like the cleverer one:

    blue   yellow purple green black
    orange   n/c    n/c   n/c  black

Now, if I power the thing up connected to a motherboard, I get pretty much what I expect from the ATX documentation I've seen, which is: Blue: -12V Orange: +3.3V Yellow: +12v Purple: +5v (STANDBY - this is always on) Green: 0.06v (POWER_ON)

However, disconnected from the motherboard, when I manually short POWER_ON to GND, I get a blip of power, but it drops straight back down to zero.

The PSU has the following label:

COMPAQ COMPUTER CORPORATION Model: HP-L1520F3P Part Number: 308446-001 Spare Number: 308619-001

It's apparently a "308446-001 HP Compaq power supply 150 Watt for Evo D530UST ultra slim desktop PC" and this is what it looks like.

You need to put a load on it. Try a fan.

Hmm, maybe I need more load? I tried two fans, but they just spin for <1sec then stop.

Oh, I tried with a little resistor/LED pair and it worked! The fans must be too small a load perhaps.

Maybe. Depends on the PSU. You can use a 10 Ohm/10 Watt resistor between 5V and GND as a load. There are plenty of instructions online.

there's normally a "power up" wire that you need to short to ground a quick google should tell you which one it is

normally green so try shorting that to ground - power should appear!

that's what happens when you press the ON button on your pooter

That's what he did. The PSU needs a load to continue running. A lot of PSUs don't work without a load.

Those are pretty old PSU's I guess, even the ATX PSU from my now dead P4 worked day and night without a load and it was a cheap ass 250w from china..

They are pretty old :) The fact it's plastered in "HP Compaq" is a bit of a sign. It's quite a neat form-factor though, so I thought I'd use it. Now to get rid of the elevendyone wires coming out of it...

That’s what he did. The PSU needs a load to continue running. A lot of PSUs don’t work without a load.

oh no it isn’t
pooter PSUs don’t switch on until told to
it’s not load dependant
it’s a command signal!

see here for the full dirt (scroll to the end for pretty pictures)

i just made a psu benchtop recently and needed to give a brown wire on the pcb a 3.3v source or it would do exactly as you are describing.

this is the instructions that i followed (minus the load resistor)


KirAsh4: That's what he did. The PSU needs a load to continue running. A lot of PSUs don't work without a load.

oh no it isn't

Yes it is. So exactly what I said in my original post then

aha - how did I miss that! are you keeping green grounded? or is it the load that keeps it going?


Yeah, I'm keeping green grounded. A tiny bit of load keeps it going okay.