On ATX power supplies the switch - if there is one - does not exactly turn 
the power supply on, but into an on state.  When you push the button on the 
computer case,  it tells the motherboard to go through the boot-up process; 
it does not turn the power supply on.  In reality, the power is always "on." 
The power supply will not go into full operation unless the motherboard 
tells it to, and there is a load on it.  (That is why it is dangerous to 
work inside a case if the power supply is plugged in.)

Go to http://www.pcpower.com/support/ATX_troubleshoot.htm for a crude test 
for power supplies.

Dean Kukral


----- Original Message ----- 
From: "Paul Hachmeyer" <[log in to unmask]>
Sent: Monday, October 30, 2006 11:34 AM
Subject: [PCBUILD] power supply question


I  recently purchased 2 Ultra power supplies from Fry's in sealed boxes, one 
a 400W one a 500W.  Should I be able to detect any voltage on the plugs 
without connecting them to a motherboard?  There is no power-on light on 
either unit, the fans do not spin up when I plug them in, the power cord is 
good.  I switched them both on/off with a working voltmeter connected to 
either 12v or 5v pins, no voltage detected on either supply.  Both set for 
110/120 volts as well.
Paul Hachmeyer

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