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My Laptop is Trying to Fly Away…

…or so it seems, judging by the excessive noise coming from my laptop’s fan recently. My Dell Latitude D820 is only a little over six months old, but in the past few weeks it has been running noticeably hotter, regardless of CPU load. Within 5-10 minutes of a cold-boot the measured CPU temperature would steadily climb to over 70°C, which was followed by the system fan stepping up to it’s maximum speed in a fruitless effort to displace heat. This abnormal amount of heat was radiating mostly from the bottom center of the laptop, directly below the CPU. The excess heat and noise were fast becoming both a nuisance and a source of concern.

I ran a full diagnostics sweep from the bootable CD, but no problems were reported. Since my initial thought was that it might be a build-up of dust inside the system, so I removed the keyboard and visually inspected the top of the system board, heat-sink assembly, and fan. The system was very clean and there was almost no surface dust, much less any considerable build-up. Unwilling to void the manufacturer warranty by poking around in a company-supplied computer, I clicked over to Dell’s webpage and initiated a customer support chat session which ended in a scheduled next-day visit from a Dell certified technician carrying a new Processor Thermal-Cooling Assembly and Fan Assembly. I wasn’t too convinced that replacement of these parts would cure my problems as the fan itself was obviously working correctly, but was just unable to keep up with the amount of heat the system was producing.

Well, as soon as the technician removed the cooling assembly the problem was evident: a massive layer of dust about 1/4" in thickness completely enveloping the inboard side of the heat-sink fins. Unfortunately there is no good way to reach that area of the computer without removing internal components, so I was unable to see it previously. Even though he replaced it with a new part, I’m sure that reinstallation of the original components would have been fine now that blockage had been pulled from the cooling system.

In the diagram below (shown without the fan assembly), the bottom and side case vents are used for intake of cooler, outside air which is forced past the heat-sink fins and then out through the rear exhaust vent.

Processor Thermal-Cooling Assembly:

image

The copper/metal hybrid cooling assembly pulls heat away from the core components, toward the heat-sink fins where the fan pushes outside air through them and out of the case. With the intake portion of the fins completely blocked the system fan would just run at full speed, but unable to properly remove the hot air from the case.

This graph shows recorded CPU temperatures over 40 minutes during idle and light-usage:

graph

The red line is before removing the dust build-up, and the blue line as afterwards. Two things are apparent from this graph, that the CPU temperature has dropped about 20°C and some downward trending can now be seen. The ‘before’ line shows that the system was fighting a losing battle against core temperature as I noted that the fan was running at 100% the entire time. But the data collected after the repair shows that even though system fan was running at very low speeds it was still able to lower temperatures quickly.

Preventative maintenance will keep these laptops running cooler over time, and in turn extend their usable lifespan. I’d recommend periodically blowing compressed air into the rear exhaust port (make sure the laptop is turned off) directly into the metal cooling fins. This should prevent any measurable build-up of dust that might begin to block off the fins entirely.

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