Dell C840 Heating problems - fixed

Question

I recently gave my son my used C840 for college and he called the other day and said it was running hotter than normal, additional heat emanating from the keyboard.  He brought it home and I was just going to clean the CPU heatsink/pipe/fin/fan and see if that made a difference.  Before the cleaning it was running at 54C with 100% usage on the CPU, after the cleaning it dropped to 48C.   Since I had it apart I decided to check the flatness of the heatsink where it mates to the CPU.  The factory heat pad on the bottom of the heatsink was all dried out and hard like glue.  I checked the heatsink with a stainless steel straight edge and I about fainted.  You could see daylight under the straight edge in quite a few places on the bottom of the heatsink.  I lapped it with 400 minus and then finished it with 600 minus (15 minutes) and re-checked it several times with the straight edge and the imperfections were gone.  After I finished I very carefully cleaned everything up with alcohol swabs and was careful to wipe down the sink/pipe/fin surfaces with alcohol also, I had powderless latex gloves on so no oil from my fingers got anywhere on the assembly.   I put a thin-thin coat of Artic 7 on the CPU with a sponge tipped swab and put it all back together, booted it up, and ran Sandra on it for five hours.   The results were pretty good the full load temperature dropped all the way down to 42C with the idle now at 37C.  If this is the first time you have had your C840 apart you will notice quickly that the CPU cooling assembly is really puny, the cooling fin assembly is puny also, and the twin fans for cooling are minimal at best.   You might want to try this if yours is heating up and you have already cleaned the fans and fins.  If you have questions let me know...... Message Edited by Broadband2 on 04-07-2007 02:51 PM

The_Penguin · Answer

Great info, thanks for posting.  My 840 hovers from 58-65 even when I configure the fans using I8KFanGUi.  My wife's sits below 50 always. I was just about to disassemble, clean and apply some heat sink compound. I'll check to see how flat things are.   Dumb question... what is 400 minus?

Broadband2 · Answer

400 minus wet/dry sandpaper and 600 wet/dry sandpaper.  I used a combination of first dry sanding it on both the X and Y axis and then switched to the 600 wet for the final finish.  I was very carefull after I was done to make sure that I got all of the sandpaper and metal residue cleaned from the heatsink.  I let it run all night last night with Sandra and it did warm up to 44-45C for a bit.  It did make a difference....   Let me know how you come out?  I am using the same fan controller and thats what I have been tracking the temps with...

The_Penguin · Answer

Thanks. I figured it was wet sandpaper, just never heard the minus term before.

Well I did it. Man, what a significant difference!!

I peeled off the thermal pad, and cleaned the surface. It was pretty flat, so I just did a quick polish with 600 grit wet.

Cleaned the CPU core with a pec pad and 100% ethanol. Applied a thin layer of Arctic silver 3 (I don't think it's really any better than ordinary heat sink compound, but that's what I had on hand) and re-assembled.

With the fans on full before, it wouldn't get below 65. Now with the fans on "normal' it's hovering around 48.

I'm not sure sanding bought me much, probably removing the pad and applying compound helped the most, but I'm sure it didn't hurt.

I'm glad I read your post, as it motivated me to finally do this.

Message Edited by The_Penguin on 04-08-2007 12:44 PM

micaradu · Answer

What processors do you guys have?I have a c640 wich stays about 48-55*C when idle, 55-65*C on light load and up to 84*C on full load so i was wondering if this is noemal for a c640.Also can you please tell me what do i need to look out for when i'll open my laptop. Thanks!

The_Penguin · Answer

Mine's a 1.8GHZ.   Also make sure your fans/cooling fins are clean.

Locked Topics – Laptops General

Was this post helpful?