CPU fan goes crazy on Dimension 8400

You can try Core Temp HERE or HWMonitor HERE.  Don't know if either one supports your Pentium, but it's worth a try.

Dumb question: Are you sure it's the CPU fan, and not the video card or power supply fan?

Power off and unplug. Check the motherboard for any capacitors that are bulging or leaking. They should look like perfectly round little cans with flat tops on the motherboard. If they're bulging, discolored or leaking, the motherboard may be shot.

Open Device Manager and see if any components are marked with ! or X. In that case you may need to reinstall the chipset driver.

Could also be a failed heat sink... [:'(]

When was last time you replaced the motherboard battery? <ADMIN NOTE: Broken link has been removed from this post by Dell>

If the system wasn't plugged in for 4 months, it's possible the battery died. When battery in my 8400 died, the fans went crazy.

If it's more than ~2-3 years old, it may be time to replace it. Power off, unplug and press/hold power button on the tower for ~15 sec. Open the case and remove the motherboard battery. Press/hold power button again for ~30 sec. Install a fresh CR2032 3-volt coin cell battery (~$2-$3 at discount stores) -right-side-up! See if that helps.

Ron

:emotion-9: Programs are not supporting my processor, it is too old I think.

Yes, I am sure that is the CPU fan. The PSF is running at constant speed. There is no other fan in my desktop (only a rad on the chipset), as the video card is not a very powerful one.

I will look again at the motherboard to find any problem on Capacitors. I do not think I have missed one, but double check is better.

All devices are ok in Device Manager.

There is a long time i have not changed the motherboard battery, but everything was ok in the BIOS (right hour, so Real Time Clock was working fine).
Problem is that the fans don't get crazy at startup. It goes progressively noisier and noisier.

Thanks for your answer.

Ben

The 8400 doesn't have thermal sensors for the CPU, so SpeedFan is about the only thing you can use to get any temps inside the case.

Well, if it's not the battery or the chipset driver, then you have to consider the heat sink failed, or isn't installed correctly. Or maybe the fan controller is malfunctioning. It may take a few min for the system to heat up and kick the fan into high speed. You do need to be careful that it doesn't overheat so much that the CPU gets fried.

Did you remove all the old thermal paste from both the CPU and heat sink before you applied a thin layer of fresh paste? Is the heat sink locked in place?

Reboot and press F12 before Windows starts to load. Go to the Utilities partition and run the fan tests. If the fan fails, you'll need to replace it with another Dell OEM fan because they have a sensor in them. If you use a non-Dell fan you'll get a "fan failure" error every time you boot.

If you need one, a heat sink for the 8400 is $20 here (pulled from another system) + shipping, and the fan is $12 + shipping here (pulled from another system). There are probably other places that sell OEM Dell parts for the 8400 too.

Ron

Hi Ron,

There must be a way to access the CPU temperature. Otherwise, how is the chipset doing to control the fan speed? It is not doing an average count of operation otherwise, the fan will go faster only when the CPU is used at 100% for some time, and not like in my case in only a min or two.

Now, I removed the heat sink, I checked that the paste I put was on the whole CPU, meaning that it was correctly put in place. I also changed the cool paste of the Chipset, which has a much smaller radiator on its top.

When going into utility partition, all the tests are pass. Again, the high speed fan test runs at 2k RPM, the low speed fan test runs at a little less than 1k RPM. Just after the tests are pass, I can hear that the fan goes slightly faster than 2k RPM, then progressively step up. If I wait longer, I am sure that the fan will go full speed.

Thanks for your support.

Ben

Just to say, I had this problem with my Dell Dimension 8400, I replaced the heatsink and CPU with unused replacement parts (same models as originals), and the thermal paste too. Completely solved it, in my case. No loud fan for me.

Sorry that should be replaced heatsink and CPU fan*

Just because the system is monitoring the temps doesn't mean that info is available to 3rd party software. I also have an 8400 and - trust me - there's no easy way to read CPU temps. About the only thing that can be done is to mount a heat sensor probe on the CPU and snake the wire out back of the case to an external display. A number of 8400 owners have done that...

I have to agree, it sounds like you probably need to replace the heatsink and/or fan. You can probably order them from Dell Spare Parts but they're likely to be much more expensive than 3rd party source should as Centrix. You an also try Ascendtech and Impact who also sell OEM Dell parts.

Ron

EDIT: Only you can decide whether spend any money on an older system or if it's time to get something new. And I make no guarantees that a new heatsink and/or fan will fix your problem :emotion-5:

Yes, I know that this doesn't mean that the info is easily available. That's really a pity though... I just find that very strange there is no easy way to monitor this kind of issue. When I bought the computer, it was a first class one (I bought it on 2004).

I tried to unplug the fan. Boot Win XP then shutdown. This way, I could check if the Heatsink was heating... Seems ok, althought I find that the heatsink was already very hot for just 2 mins without a fan.

I wanted to buy a new sink as It was not too expensive. My problem now is that I am french and that the shipping costs are really huge. I tried to find resellers here in France but I am out of luck until now.

Well, I wanted to set up my old Dimension for my mother for which the power of this computer was sufficient. I just bought 2 Go of DDR2 533MHz to have a sufficient 3Go RAM. 

Anyway, thank you all for your help. I wanted to have a PC for just 50€, I guess I was too optimistic :emotion-9:

Do you have eBay in France? Or maybe you'll have to wait for the Euro to go way up against the U$ Dollar. :emotion-4:

Until very recently, most Dell PCs had no way to monitor the CPU temps. Leaving the sensors out was probably a way for Dell to save money. :emotion-5:

Dumb question... Are you testing the system with the new RAM installed? And are you sure the new RAM is fully compatible with the 8400? Dell PCs can be extremely fussy about RAM, even if it has the right specs for the system.

If you're testing with the new RAM installed, power off and unplug from the mains.

Press/hold power button on tower for ~15 sec.

Remove the new RAM, leaving only the original RAM in slots 1&2 (they have same color retention clips).

Now remove the motherboard battery and press/hold power button again for ~30 sec

Reinstall the battery, right-side-up!, and see what happens now.

I don't promise that's the problem, but it's worth a few minutes to check it out. And if that fixes it, you owe me a :emotion-22:

Ron

Yes, we do have Ebay in France. I have found some Dimension 8400 to buy but no luck for just a Heatsink. There is a store in the UK that sells refurbished heatsinks. 20 pounds + 5 pounds for the shipment, that is not too expensive although I don't want to spend money for nothing. At least, I can sell the DDR2 533MHz on ebay...

I tested the system with the new RAM installed, but the issue was already here before. The 2 DDRs are well recognized by the BIOS. I bought them on a website that specifies that they were compatible with the Dimension 8400. I first thought that the high speed fan was just an issue about the dust inside the PC and because the thermal grease was too old.

I have time no more to spend on the diagnosis. My Girlfriend does not like at all having an airport :emotion-58: in the lounge... My GF goes like this --> :emotion-12:

Hey BBn can we get an update here?  I'm willing to bet that replacing the cpu fan solved your probelms.  I am about to try and tackle this very same issue with a Dell Dimension 8400 and would like to know what worked for you in this instance.