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PC powers up, then shuts down ~1 sec later. Cycle repeats.

By mil0oz ·
Hi all, posted this yesterday but has been pointed out that I did it in the wrong forum. So here's take 2.

Have an issue with my PC. When I press the power button, the machine whirs into life for just short of a second. Then dies. After a ~2 sec delay the process will repeat. This will continue until the PSU is switched off or the main supply removed.

I have removed all connections in an effort to identify where the issue is arising (HDD/GPU/RAM/Floppy etc.). With just the mobo and PSU, when pressed the power will remain on.

However, the moment I connect the CPU power supplies (from the PSU) to the board the aforementioned problem arises. For what it is worth this CPU lead comprises two 4-pin female connectors, marked CPU1 & CPU2 respectively. When this error occurs, literally the only things runnng are the PSU and mobo. It's when I hook up the CPU connectors that it occurs. So no RAM, HDD etc. etc.

I have tried removing the CMOS battery and removed and checked the distance from the mobo to the case in case of grounding and have removed, reseated and repasted the CPU & CPU heatsink.

System stats are as follows:
Intel E6400 2.13GHz
Gigabyte DDR2 Mobo
9800 GTX GPU
4Gb DDR2 RAM
850w PSU

Thanks in advance for any help,

Christian

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All Answers

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PSU or Main Board

by TheChas In reply to PC powers up, then shuts ...

From the description, the problem could be the PSU or the main board.

I'm leaning toward the PSU as a motherboard problem would be more apt to just shut the system off and not cycle. Plus, from a testing stand point, it is easier to swap in a new PSU than the motherboard.

However, if this is a new system, the first thing to check is that the 2 CPU power connectors are properly wired.

What I suspect is that the power supply has lost the ability to supply the rated power on at least one of the outputs.

On initial power up, the primary voltages on the motherboard are good, and the power good signal is valid. When the CPU section powers up, one or more voltages drop below limits and the power good signal goes to invalid and tells the PSU to turn off. When the CPU power circuit shuts down, the power line switches back to valid and tells the PSU to turn back on.

Before you do get a different PSU though, inspect the motherboard for any signs of damaged components. Look closely at all of the filter capacitors. (Round cylinders with silver tops. If any of the tops are crowned up or it looks like liquid has leaked from the part, then your problem is with the motherboard.

Chas

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Right

by Mohammad Oweis In reply to PSU or Main Board

i agree with you, its either the PSU or some capacitors in the MB.
Try to borrow a PSU from one of your friends with the same power rate, and test it in your system.
if its some capacitors they can be replaced, ask a technician to do that.

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Thanks

by mil0oz In reply to Right

Thanks guys. I'm going to get a decent pen torch from my father and have a good look at the capacitors.

If they all look OK I'll take it to a chap I know who will have another PSU I can try.

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Just in addition to the above

by OH Smeg In reply to PC powers up, then shuts ...

I have seen this with several Gigabyte M'Boards recently with Plug In Video Cards. The Video Card needs to be removed and the contact edges cleaned with a soft Rubber/eraser then refitted.

The system then will boot normally.

Col

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PC powers up, then shuts down ~1 sec later. Cycle repeats.

by wysetech2000 In reply to PC powers up, then shuts ...

Hey Christian: From your description of the problem i would think that either your PSU is very weak or the motherboard has an internal short circuit.

I would try a known good PSU first and if it acts the same the motherboard is most likely the culprit.

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