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Intermittent Power Up

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#1 tharpdevenport


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Posted 16 January 2016 - 08:57 PM

A couple days ago this HP computer tower (not a laptop) started having trouble powering on.  You'd press the button on the tower, it would light up, start doing it's thing, then shut off.  You have to keep trying until it stays on.


So far, no loss in power while in operation.  No other issues.  Restarting isn't an issue.


The cooling fan in working (and the temp' is good). I scan and make sure the computer isn't infected each week and I just did a thorough scan Friday. No new hardware. Only one new program installed (Speccy) but the issue occured before the new program was downloaded. No Windows Updates made.


I could try switching out the power cord, but I'm worried if there is an issue that could get worse, the comptuer won't come back on and at the moment, that leaves me unable to turn off the computer at least for two more days (no need to go into the details about that) because it will be needed.


I don't know if this makes a difference, but when thunder/lightning storms are coming threw, on top of simply shutting it down, the power cord is unplugged from the back of the tower (would doing this maybe screw it up?).


About a year and-a-half ago the heat sink was cleaned, a new cooling fan put in, and I assume the inside was blown out for dust (though it probably needs it again, but like I said, I can't shut it down right now).  Plus, I'm just guessing at issues based on comments from other people.



What do I do now?

Edited by tharpdevenport, 16 January 2016 - 09:42 PM.

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#2 mjd420nova


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Posted 18 January 2016 - 08:01 PM

A little bit of dust can go a long ways, after 18 months, certainly.  Yes, it is a good idea to unplug, not just shut down your PC during lightning events.  Intermittent events within a dusty power supply can cause unrelated faults.

#3 dc3


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Posted 19 January 2016 - 01:07 PM

Please post the model of this HP desktop computer.


If I understand this correctly, the problem is when you first start the computer.  But after it has been running there is no problem restarting it or starting it with the power button.


If this is the case this could be a problem with the motherboard component that initially fails when the computer is first started.  Once the component is warmed the problem no longer persists.


When you press the power button this causes the motherboard to short the green wire and a black wire in the 24 pin connector from the PSU.


You can test to see if this is the motherboard or power button that is causing this by bypassing them.  


With the computer shut down and the power switch to the PSU turned off  open the case.  


Caustion:  You need to discharge any static electricity in your system by touching the bare metal inside the case.  Electrostatic discharges can kill board components.


After you have open the case remove the 24 pin PSU connector.  (There is a clip on the front of the connector which has to be depressed in order to remove the connector.)


Take a paper clip and press one end of it in the socket for the Green wire, plug the other end into the socket of any black wire.


Switch the PSU on.  The case fan/s should start immediately if there isn't a problem with the PSU.  If this works from a cold start I would then suspect a problem with either the motherboard or the power switch.


If you have a multimeter you can set it on the Ohm scale to test the power switch.  With the computer shut down and the PSU power switch turned off place the leads from the meter on the two header pins on the motherboard where the power switch is connected.  Press the power button, the Ohm scale should zero out or very close to it.  If this happens and the PSU worked with the two wire shorted out I would suspect the motherboard.

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