Member Avatar for autrakis

my computer shut down for an unknown reason. i've checked all of my power connections, which are good. i know power is being received by the machine because the stand by and memory power LEDs are lit on the motherboard . however, the main power LED is not lit. so is it my motherboard that has a problem or the power supply?

thanks,

ted

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Short summary: the standby and memory LEDs being lit only prove the board is getting standby power (the +5VSB rail) — they do not guarantee the PSU is putting out the full set of stable rails or that the motherboard can complete POST. This expands on , and by giving a safe, ordered way to diagnose whether the fault is the PSU, the front-panel/switch, or the motherboard.

Quick diagnostic checklist (do these in order):

  • Power off and unplug. Do a visual inspection of PSU and motherboard for bulging caps, burn marks or a smell of burnt electronics.
  • Test the PSU off the board: with the PSU disconnected from the mobo, use the PS_ON-to-ground short (paperclip) to start it and see if fans spin. This is only a basic check — it does not prove the PSU is good under load. If comfortable with a multimeter, measure +12V, +5V and +3.3V while the PSU is running; if voltages are missing or PWR_OK never goes high, replace the PSU.
  • Try a minimal boot: with power disconnected, remove all drives, add-in cards and all but one RAM stick. Re-seat CPU cooler and power connectors, then try to start on an anti-static surface (outside the case) to rule out shorts.
  • Check the front-panel header: unplug the case power switch and short the two power pins briefly with a screwdriver to simulate the button. If that starts the system, the case switch or harness is faulty.
  • Follow ’s CMOS hint properly: power off, unplug, remove the CMOS battery for ~5–10 minutes (or use the clear-jumper per the manual), then restore and try again.

If the PSU shows correct, stable voltages and the board still won’t start after the minimal-boot and CMOS clear, the fault is most likely the motherboard (VRMs) or CPU. Given the age of many systems, capacitor or VRM failure is common and usually requires PSU replacement first, then mobo replacement or RMA if available. Keep safety first: if unsure about live-voltage testing, seek hands-on help.

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Member Avatar for crunchie

Hi and welcome to the Daniweb forums :).

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Impossible to say really with any real conviction. If it were me, I would be trying to borrow a psu to see if the fault lies there.

Member Avatar for autrakis

crunchie,

i'm hoping it is the PSU, but would the LEDs for power stand by and memory be on if it is a PSU issue? I was thinking it was a motherboard issue. thanks,

ted

Hi and welcome to the Daniweb forums :).

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Impossible to say really with any real conviction. If it were me, I would be trying to borrow a psu to see if the fault lies there.

Member Avatar for crunchie

Different wires from the connector power up different things.
I am just saying what I would try first.

Member Avatar for Duleee

Try to clear CMOS can be one of the reason.

Member Avatar for paulas24

i would like to agree with crunchie about the psu if not you should check the power switch.

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