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Wondering if anybody has experienced the following issue

  • Shutdown Windows,
  • PC shuts off,
  • Motherboard Start LED remains lit
  • Turn off Power via PSU rocker switch
  • Motherboard LED takes 2-3 secs to extinguish.
  • All good so far.
  • With the power switch still off the Motherboard LED lights up again for 2-3 before finally going out until power is switched back on

My question really is why did the motherboard LED come back on for a second time even though the power was off?

Mobo is ASUS Crosshair V Formula Z.
PSU is Coolermaster Silent Pro 750w.

PC is working absolutely fine, just wondering why this would be the case?

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The power supply (PSU) has capacitance. The rocker switch on the back disconnects the power supply from mains, but there is still plenty of electricity stored up in the capacitors to power a LED for a few seconds.

You didn't specify, but I'm assuming that you pressed the power button again?

It is good practice before working inside a computer to turn the machine off, flip the power supply rocker switch to off, then press the power button again.

This is what I do, and I always see the behavior you are describing because of the energy stored in the PSU capacitors.

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  • Hey spuder thanks for the info. Pressing the power button on the front of the machine does not seem to change the behavior. I know what your saying about the capacitance but find it strange the LED would go out a couple of secs after the psu rocker switch is set to off, only to come back on again for a couple of secs before going out again. I'm a newbie to all this and maybe reading too much into things!
    – Richie
    Commented Aug 13, 2013 at 9:30

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