Optiplex 390 Not Powering Up (No Lights When Pressing)

Question

story short - my Optiplex 390 doesn't power up:

So when I connect the mains power cable, the fans run for a second while the power button lights up amber and then blue, then it all turns off. Pushing the power button does nothing.

If I disconnect and reconnect the connector from the power button to the motherboard, the same sequence with the fans and power button lights happens.

Whenever the power is connected, the orange motherboard light is constantly on.

I've replaced the power unit with a tested second-hand unit, and the problem persists.

What could this be? Could it be as simple as a defective button? I don't think it's the motherboard as the constant on orange light means it's getting power right?

Thanks

redxps630 · Answer

orange light on motherboard on only means there is minimal 5V to board.  PSU can still be failing.  Are you sure the test psu is working?  The only way to confirm or r/o psu issue is to test your 390 w a working psu either new or transplanted from another working system.  If a confirmed good psu still can not power on 390, next thing can be motherboard component failing.  again orange light on or fan on is not sure sign of board health.  of course theoretically the button itself or front panel small circuit board can also be bad, but those are less likely than psu or motherboard component statistically.

Daheem24 · Answer

Thanks @redxps630 . I'm certain that the PSU is working, so I've ordered a replacement motherboard. Fingers crossed that'll do the trick.

Daheem24 · Answer

I've just put in the replacement motherboard (tested) and still no luck.

However, when I connect the mains power this time, the amber light on the power button and the fan don't come on for a second. Instead it's just a short hum from the PSU.

What do you think is happening here?

redxps630 · Answer

I would test the board w a 100% definitely working psu.  how were you sure the psu was good, what test was it based on?  to me the only reliable test is that psu pulled from a currently 100% working system (or brand new out of box).  you could spend whole day trying to trouble shoot, but you might kick yourself if it turned out to be as simple as a failing psu.

Daheem24 · Answer

So I did the 'paperclip test', video'd here: https://www.youtube.com/watch?v=ixcWCrYpw3Y I assume when the seller said this was tested, this is what they also did?

redxps630 · Answer

The paperclip test is meant to turn on the psu w a load. It is not a test to show psu is supplying the correct volt/current to turn on motherboard. A failing psu can still turn on fans. testing psu is not as simple as testing light bulb.

btw without a load, psu would not turn on, whether it is good or bad.

Daheem24 · Answer

Aah okay thank you. So for my understanding, when you say the PSU won't work without a load, whats the load here? Is it the motherboard?

redxps630 · Answer

yes. load is like a resistor.

prodigy28 · Answer

replace the power button

Computer Guy · Answer

Had the same thing happening to my OptiPlex 390, and when I took the front bezel off, I was able to push the power button and it came on.  The plastic button wasn't applying enough force on the power button.  I just put a small piece of double-sided tape and left the part that touches the button covered with the plastic tape.  Can't see the power light, but that's no big deal.

abumasnur · Answer

I created an account on Dell just to give kudos to you. You were right about it being the button not applying enough force. I put some foam with a hole in it so that the LED still get's through just enough to be visible.

Optiplex Desktops

Optiplex 390 Not Powering Up (No Lights When Pressing)

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