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Old 12-04-2012, 08:23 AM   #1
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Default PSU or Mainboard? Can't turn on PC anymore

Ok let me describe the issue:

I have an older Asus P5E board which already showed early signs of this months ago.

The issue was that manually shutting down my PC via case button resulted in that the comp couldnt be switched on right away, I needed to discharge the PSU by turning off the PSU, then press case button for approx 15 secs.....then wait for a flash on my USB lighted keyboard - THEN i was able to switch the computer on.

When i just powered down the machine from WIn7, i didnt have any such issues, the comp usually turned on fine every morning.

TODAY, my cats went nuts, i have this "awesome" case with the power button on top, resulting in my cats turning off the PC today multiple times by jumping on it.

NOW - I cant turn on the machine at all anymore.

I reset CMOS and checked seating of some components. All i see is the SB_PWR LED on the mobo flickering (not blinking!!) which look very much like a 50hz flickering to me.

The "correct" state of the SB_PWR LED is unknown to me,i assume solid light?

I have hope that this issue might correct itself by leaving the PC off for some hours....but if not, I need to know whether this is a PSU problem or a mobo problem.

When i do research online i always see references that its related to overcurrent on the 5V standby line, but then they are talking about a SB_PWR LED blinking, not fast flickering like mine does.


all my components are high quality, the board is an Asus 5E deluxe and the PSU a 750W toughpower.
ASUS Rampage Formula - Q6600@3.6Ghz - Win7 x64
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Last edited by flexy; 12-04-2012 at 08:27 AM.
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Old 12-04-2012, 08:46 AM   #2
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Smells like the psu. What is the make/model/year?

Check the voltages on the 3.3v, 5v, and +12v rails and ensure that they are within acceptable (usually +5%) ranges.
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Old 12-04-2012, 09:07 AM   #3
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You don't suppose the kittys broke the actual case switch...?
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Old 12-04-2012, 11:04 AM   #4
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The newer model of kitty cats don't have that problem as much.
I recommend picking up a spare PSU, such as:
$19.99 after coupon + MIR, with free shipping.

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Old 12-05-2012, 07:46 AM   #5
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It's not that easy.

I read several guides now trying to determine whether it's a PSU issue or a motherboard issue.

When i unplug PSU from the board, jump the PSU plug (green/blk) and them measure 5VSB it looks fine, i see the 5V. I can jumper the PSU and then get PSU fans and the still connected fans etc. going for approx 5 secs.

Problem starts when i plug in the ATX connector the board.

As i mentioned earlier, SB_PWR LED is flickering 50hz and I measure the 5VSB power line at 2.6V, and PS_ON at 1.8V

Pressing the front panel button should lower PS_ON to 0V, but pressing the button doesn't change any voltages. (It's corrected right tho).

Also grounding PS_ON "manually" while everything is plugged in doesn't do anything.

I also measured PWR_OK (while anything is plugged it) which should jump up after I turn on the PSU indicating that all rails are in spec, but it's constantly at 0V.
ASUS Rampage Formula - Q6600@3.6Ghz - Win7 x64
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Old 12-05-2012, 04:39 PM   #6
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@flexy: you need to simply swap out the PSU with a "known good" spare one.
That should provide a better diagnosis than whatever you're trying to do.

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