Member Avatar for gixermann

I recently obtained a used P35-609. The problem im having is getting it to power up and stay on longet than 5 seconds. Oddly if I enter into BIOS at power on it will remain on. Thus far iv left it on for 20 min. Iv tried removing reseating devices, no luck and no change. Hopefully someone has ran into this problem or at least heard of it and conquered it.
Any and all help is greatly appreciated.[

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A concise diagnostic summary and next checks for a board that powers off seconds after start but stays powered when halted in BIOS. Earlier posts from and covered isolation and cooling checks, and reported a later successful swap; the items below focus on measurable tests and visual checks that were not covered in detail.

  • Measure the main rails at the 24-pin while the board is powered. Use a DC multimeter to note 3.3V (orange), 5V (red) and 12V (yellow) relative to ground. A rail that collapses or spikes right before shutdown points to a marginal PSU or a heavy load/short on the board. For safe measurement technique see the guide linked below.
  • Check PS_ON and 5VSB behavior. With the PSU plugged in but soft-off, 5VSB (purple) should be present; when the power button is pressed the PS_ON (green) should be pulled low. Abnormal signals here indicate the PSU or the motherboard power-control circuit.
  • Rule out a chassis short: bench the motherboard on a nonconductive surface (cardboard) with minimum connectors attached. Inspect the back for misplaced standoffs, solder splashes, or anything making contact with traces.
  • Inspect power-delivery components closely: VRM mosfets, chokes and electrolytic capacitors. Bulging/leaking caps, cracked solder joints, or heat-damaged components are deterministic signs of a bad board in this era (see capacitor background link below).
  • Verify front-panel wiring and POST indicators. A stuck or wrong-wired power switch, or a diagnostic LED/beep code, can reveal a control-level shutdown rather than a voltage collapse.

If measurements show the rails collapse at shutdown, the PSU is implicated; if rails remain in-spec, the fault is on the motherboard (VRM, short, or power-control logic). Working on PSUs and live rails involves mains risk—exercise caution or consult a technician.

Further reading: How to test a PC power supply with a multimeter () and background on era-capacitor failures (Wikipedia: Capacitor plague).

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Member Avatar for Capt_Kirk

That usually indicates a dead componet, Have you tried removing everything except the CPU from the mobo? if it will stay up you can add componets back until you find the one that kills it. If it still has problems when everything is removed then your mobo is bad.

Member Avatar for Dend78

is the heatsink seated properly to the CPU? stupid question but its been done, i had one doing it for a while couldnt figure it out it would run for about 10 min or so trying to install windows then it would shut down as soon as the load put a little bit of a strain on it, then it would shut down from overheating. it would enter bios just fine and everything and it would be fine but when you stressed it a bit off it went. just a place to check thats simple.

Member Avatar for gixermann

Sorry it took so long to post. I did remove the heat sink, cleaned it, apllied new heatsink and nodda.. same problem continues. Thanx for your efforts all but im giving up on this one and resigning to a MB prob. At 200.00 a pop its safe to say iv sold it for parts..

Member Avatar for webstrand

I had the same problem, i just replaced the power supply and it worked like a charm.

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