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Desktop CPU Fan Problem

I have just replaced the psu on my HP PC. The PC went dead and the new psu brought it back to life. Now, almost exactly to the minute when the PC runs for 2 hours, the cpu fan starts running super fast, from 1600 rpm's to over 3600 rpm's even though the cpu is not getting hot. I checked all the voltages and they are on the money. To make things stranger when the cpu fan goes to this high speed for no reason, if I put a load on the cpu the fan slows, yes slows, down to the 1600 rpm speed. This driving me nuts. I have cleaned out the MOBO and air sprayed the entire area thinking it might be a dust problem but no help.

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  • Ron Goldstein Jan 08, 2008

    the psu was an aftermarket and no the cpu is not clocked

  • fp01 Feb 06, 2008

    Simular problem here. All three fans (pre and post CPU and powersupply) goes up to maximum and back randomly. CPU load is zero, no programs running, all is really cold inside. What is causing the system to belive it´s red hot, where is the sensor placed?

  • Ron Goldstein Feb 06, 2008

    No it was an after market psu and no overclocking.

  • fp01 May 11, 2010

    Sorry, forgot: Computer is a HP/Compaq DC7100 desktop P4 3,2G
    Nothing is replaced or altered from original configuration. No dust or dirt inside computer.
    If it´s the bios, how could it work fine for two years, then suddenly start to rush the cooling fans up to maximum?



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My first check would be to see if the manufactuer has a BIOS update for the ma inboard that resolves that problem.

If they don't have one available on their website I would contact their technical support because it may be a known issue that they are currently working to correct.

At least knowing you'll know that a fix is only a few months away.

If the manufacturer claims that your problem can't be verified you may have a faulty thermal control unit on the mainboard.

Let me know what you find out.

Posted on Jan 08, 2008

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Was the psu the exact replacement?did you clock the cpu?

Posted on Jan 08, 2008


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Hp P6000 fans stop after 15 seconds. Hard drive light stays on. nothing on monitor

dead PC, DESKTOP PC ,as old as 2009.
the fans tells you the PSU shut off, for cause.
fans, so you saw all fans turn off or just 1. or 2 of 3.
my pc has 4 fans many have 3;
CPU fan stops ,cpu overheats , PC goes slow or dead. clean the lint off it.
GPU fan , video goes dead. if it overheats.
PSU fan is inside the PSU if it goes bad, PSU is bad.
no monitor stated, is it CRT or LCD is it 15 years old.
if the monitor is 2002 or newer the OSD screen works
even with PC turned off, press the select button see that OSD screen ? telling you the monitor is not dead in 1second flat;
i caN NOT understand why the HDD lamp glows,
if the PSU shuts off , most LEDs go dead, on my PC
the standby LED on the MOBO glows, unless you pull the PSU power cord.
your HP PC came with 9 different mobo, during its production run.
at least. so answers come harder from that reason.

here are some simple tests.
test 1
power on, hear fans run
does the DVD drive (or cd) button eject work,.?
do all fans not just 1 or 2 worK? look for all fans clean the lent out
or things will overheat,
PSU can be bench tested or in the PC case.
using a jumper wire, even the HP service manual covers that.

power on the PC (after keeping monitor on for 5 full minutes)
test 2
the Screen must say, "hit ESC key to enter HP setup" BIOS.
press the ESC key on the monitor
if no text shows up that is a dead PC< "text above missing{"
if the PC told you to hit another key do so.
The ESC key , activates the BIOS brain. this cause
all those pages to work as seen in your service manual;.
if BIOS is dead that is a bad PSU (monitor ok)
or CPU is overheated.
bad ram, take all sticks out and test 1 by 1, ask how. !
The PSU will shut down on up to 12 or more faults
but never shuts down the standby power bus. unless AC line pulled.
IF the PSU has fan as most do this is the first place I look.

try this guide

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1 Answer

I got the old desktop from my husband after he bought a new gaming pc. He reused the old PSU, so I bought a new Corsair CX600 PSU. After installing the PSU into the desktop, we tested it and every thing...

The motherboard is no spring chicken, so there is a good chance that it has given up. Check the capacitors around the CPU socket. They are between the socket and the back panel.They should all be flat or dished inwards. Although there are a couple in the area of the power plug. This is the first place to look as it is an area that has been disturbed. If they are not as I have described then you could replace the blown ones but there is no way of telling what other damage has been done.

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"i can find my dmm?" did you mean CAN'T?
"its clearly off", what is off?
the fans are 3 pins,2 are power, one is RPM tachometer.
"it all works fine", so you can boot and run any OS, ?

"the voltage reads +12vdc", where, at fan or PSU?
the fans run off 12vdc, they are DC motors (from outside fan)
if the fan runs slow at 12vdc the the fan is bad or is a low RPM
fan, as some are, bigger fans run slow, for less noise.!

first is the CPU fan it must run full speed, if not the CPU will overheat in seconds and ALL CPU shut them selves (by there selves) this way. so CPU fan is first. what does it do... there....?

then BIOS screens. GOT BIOS UP? and running? with, ESC key pressed>.
let me guess your symptoms
1: PC dead. will not boot.
2: BIOS dead.
3: all fans DEAD,.
4: power switch works and all PSU voltages read right, (seems not)/?
5: if the PSU power wire reads right(DMM), matching the side sticker voltages, and the CPU is dead, the MOBO is dead, or CPU is toasted.

here is a modern PSU, sticker.
see 5 to 10 power lines, see them. all must read correctly
if a fan is dead, then its dead if 12vdc is present on the fan power pins.


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the fans are dead. right? why not start with sounds.?
Desktops have 2 or 3 fans
1 in the PSU that must run fast,. does it ,heard and seen?
2: the CPU, has fan for sure, and must spin, blow air across the CPU heat sink not packed full of lint all PC this old ,always have,
3:then the GPU video card may have a fan that again must work.
so if all fans are dead, the psU IS BAD,


answering for
dead PC
dead black screens, never any text.
no sounds from PC
no monitor stated(i'd need that if the PC made sounds)

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Computer won't boot - fan on cpu does not run - cd drive does not power up -


If there is no sign of life, then it is usually a power supply problem. Check PSU connector. If PSU fan does not turn on check the power cable. If power cable is good, test power from PSU using a multimeter and eventually replace PSU.

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