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FREQUENTLY ASKED QUESTIONS
Power Supplies
Last updated: 4/13/05
Q. How can I "trigger" an ATX power
supply to test it?
A. Do this at your own risk...
- Is the power cord plugged into the power supply? Is
the surge protector on?
- Is it plugged into a live outlet?
- Plug the power supply AC power cord directly into a
wall outlet.
- Many recent ATX power supplies have an additional power
switch on the back of the power supply itself. Is it on?
- Is the power supply set for the correct voltage? Most
of them have 110/220 Volt switch. The 220 volt setting won't work
in the U.S.A. The 110 volt setting in Germany, for example, will
probably fry the power supply--I've done it!
- Unplug the power cable to the power supply and disconnect
all of the power cables from the power supply except the main power connector
to the motherboard. Disconnect all other cables to the motherboard
except the front panel power-on connector. Remove all expansion boards
from the computer. Push the power-on switch and see if the power
supply fan turns.
- Try another outlet.
 Now
to answer the question... Unplug the power cord from the power supply, short-out
pins 14 and 15 on the power supply main power connector, and plug-in
the power cord just long enough to see if the fan is working. This
may not be the best thing to repeatedly do to an ATX power supply (it
can damage it). The ATX12V Power Supply Design Guide states
that the power-on function should be normally done with TTL (transistor
transistor logic) circuitry which pulls pin 14 low. I use a jumper cable with alligator clips
at each end with partially stretched-out paper clips in each alligator
clip (an old trick). Pull the power plug before removing the jumper. If
the power supply works, remove the motherboard and see if it is shorted-out
by a stand-off or lose screw. I have seen cases where a particular "good" ATX
power supply would not work with a particular "good" motherboard--so
much for standards and design guides.
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