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Intermittent post failure, random display fail

Last response: in Memory
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February 18, 2011 4:34:30 PM

hi all. could you please help me diagnose this prob with my system..

specs:
Asus P5KPL VM (intel G31/ICH7)
1 gb ddr2 800mhz ram
no addon graphics/sound card

a while ago my motherboard stopped posting intermittently. it would either give no beep at all or it would post normally, boot the os and then after a random amount of time, act as if it had gone into standby..i.e. cpu fan spinning, hdd spinning, no display or sound. sometimes the display would give static.

i sent the mobo for repair and they gave me a replacement of the same model(not new, previously repaired).
now the replacement has pretty much the same problem except that when the problem occurs the monitor instead of going blank shows 'Sync out of range' and there's static coming from the speakers.

just now it happened again and here's what i did:
switched off power, switched it back on and gave it try. no beep and hdd not spinning up.
took out ram, reseated it and tried it. posts normally. because of this i think its a ram problem. also, right now i ran memtest 86+ and it showed my ram as ddr2-400. i'm sure i have ddr2 800mhz. further, the prob occured within a minute while testing the ram and this time the monitor showed static.

i'll get another stick to test tomm, but till then any advice? could it also be a prob with the dimm slot? or the mobo itself?
a c 346 } Memory
February 18, 2011 5:02:35 PM

Welcome to Tom's Forums! :) 

Before and now, this is typically symptoms of a failing PSU. Try another from another computer. or purchase one from a company allowing returns in case it's not a bad PSU.

I prefer single rail, Japanese capacitors, and fault protection; e.g. Corsair PSU.

If it were a new rig then I'd look for a short/grounding short:
Lazy-Man's breadboard: Unscrew all of the MOBO + PCI screws, 1 stick of RAM, and dangle the MOBO supported by a towel {away from anything conductive e.g. case or I/O shield}. Also, if you have an after-market CPU fan then look at the mounting bracket underneath the MOBO - if there's no plastic/rubber in between the mounting bracket and the MOBO then add plastic washers: Mounting | washer | MOBO.
February 18, 2011 6:15:00 PM

i dont think its a psu problem..i tried an old one that i know works( a friend's ) and also bought a new one.
i've also tried hooking up the mobo while its not screwed in. i placed it on a chair in its box. didnt work. the cpu fan is what you get with the intel cpu ( Pentium D 820 2.8Ghz btw).

also, would a failing psu explain the static on the monitor and through the speakers?
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a c 346 } Memory
February 18, 2011 6:45:45 PM

Based upon what you've said you done, that leaves the CPU; process of elimination.

Suggest that you unplug everything including your Keyboard & Mouse, and remove any PCI Card(s), 1 stick, remove ALL header connections (e.g. USB, Speaker, etc) use a wire or screw driver and short (close circuit) on the PW+/PW- to see it it boots.

Failure - after new MOBO & RAM leaves the CPU. :( 
February 19, 2011 4:24:56 AM

as i understand a cpu would either run properly or not run at all right? i mean it would not fail randomly.
also, the replacement motherboard is not new, its one that was repaired earlier. its not out of the box. the ram is also around 4 years old.
and how will trying to boot a minimal setup help diagnose ? the system boots even now sometimes. as i said, i'll get another stick of ram to check today.
a c 346 } Memory
February 19, 2011 11:35:04 AM

You decided it isn't the PSU...as I first said "Before and now, this is typically symptoms of a failing PSU."

I've seen a bad, shorted, USB mouse cause a full post failure.

What I'm trying to get you to do is ELIMINATE the variables in a very long equation of multiple components and interconnections to determine the ROOT CAUSE.

Example: faulty-> power button, wiring, short, RAM, PCI, you name it.

Oddball 9/10 is from a failing PSU.
!