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OptiPlex 755 Mini Tower won't power on, no exterior lights

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I cannot get an OptiPlex 755 Mini Tower to power on. It had been running fairly continuously in an office environment on a APC battery backup/surge protector until it failed Monday morning. Then there was some orange light that was flashing or continuous. When the computer was turned off, it would not come on again. Sorry for the vagueness, but this is second-hand information. I found a fair amount of dust inside, but I've seen far worse on computers

When I push the power button I get no change: no light in the power button, no diagnostic lights, no sounds, no fan movement. When I connect it to power the "AUX LED" light on the motherboard comes on a solid yellow/amber so the PSU is putting out something.

Is this likely to be a PSU problem? Is there some way to pin it down other than buying a replacement PSU?

Thanks for any help,

Joe M

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RE: OptiPlex 755 Mini Tower won't power on, no exterior lights

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* Disconnect the power cable from the rear of the computer and from the outlet or surge protector
* Open the computer cover
* Disconnect/reconnect the main power supply connector to the motherboard
* Press and hold in the computer power button for 10 seconds
* Replace the computer cover
* Reconnect the power cable to the rear of the computer and directly into the wall power outlet
* On the rear of the computer, look at the power supply for a black button
* If present, press the black button, does the LED come on?
- If no, the power supply is defective and must be replaced
- If yes, the power supply is good
* Attempt to power on. Check the power supply to see if its fan spins or if any other fans in the computer spin


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RE: OptiPlex 755 Mini Tower won't power on, no exterior lights

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Chris,

Thanks for answering. I tried most of the steps with no change in behavior -- internal AUX LED on motherboard comes on when PSU plugged in, no fans, noise, or lights when power button pushed.

Unfortunately there is no test button or LED on the back of the power supply (Model L305P-01, Part NH493, CN-0NH493-72435-840-2226, Rev A05). Dell must have changed power supplies later on.

Does this test and result give any further information about whether it is a power supply failure or not?

I also disconnected the power supply and tried the "paper clip" short of the P1 green wire to a black wire. No sign of life in the power supply. Should this power supply react to the paper clip test?

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RE: OptiPlex 755 Mini Tower won't power on, no exterior lights

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Sounds defective to me. Not sure about the paper clip thing. A replacement NH493 cost $29.95.


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RE: OptiPlex 755 Mini Tower won't power on, no exterior lights

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Thanks Chris,

Ordered a power supply.

The "paper clip" test connects the green wire to a black (ground) wire on the main connector going to the motherboard. This supposedly mimics what the front power button does. It causes most ATX power supplies to bring power to the fans and connectors.

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RE: OptiPlex 755 Mini Tower won't power on, no exterior lights

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Thanks for that explanation. I had seen other users test in this way but could not find any Dell KB detailing it.


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