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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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