Friday, January 14, 2011

Keeping your cool

I started ripping some DVDs. This is something I explored years ago, but the quality of the rips just wasn't there. I tried ripping Shrek and found that color reproduction was poor. Things that appeared as smooth color gradients on the original DVD were dithered when I played the rip. I was driving the TV using a DVI -> HDMI connection from a PC. I abandoned that as unsuccessful.

Now we have a better ripping S/W and the capability to run a DLNA server to deliver the content to a Playstation 3 for viewing on an HD TV. A little experimentation revealed that all of this seems to provide an acceptable reproduction of what I see on the actual DVD. That's important; otherwise I would stick with just playing the DVD. But the media server is a subject for another blog. This is about what transcoding does to a PC.

Since transcoding DVDs is a pretty compute intensive process, I chose the most powerful systems at hand. Those are a couple laptops equpped with Intel Core 2 Duo processors and a desktop with an AMD Athlon. (The athlon is actually pretty ancient, but it's dual core and available.) The first thing I noticed on one of the laptops, a Dell Vostro 1700, was that the CPU temp shot up to 90° C and continued to climb. At 93° I stopped the transcode for fear of doing damage. I asked around (Notebook Review forum) and the general consensus was that this was excessive temperature. Likely causes would be blocked cooling vents and/or poor contact between processor and heat sink.

Next step was to disassemble the Vostro down to the CPU cooler. This is what I found. That's a wad of dust blocking the cooling fins.

The conductive paste on the processor looked like this:

The rapid temperature rise led me to suspect that there was not good contact between the cooler and the CPU. They used plenty of paste during assembly, but it didn't seem to form a thin film. I cleaned that up and reinstalled the CPU cooler with a small drop of Artic Silver.

The result of that was that idle temp dropped from 47° C to 40° C. While ripping and transcoding DVDs (which loads both cores) temperature rose much more slowly and leveled off about 80° C.

The next thing I tried was undervolting the CPU using the instructions here: and additional information from That brought idle temps down to 34° C. CPU temperature while ripping/transcoding remained at about 80° C.

Transcoding on my T500 also drove temperature up to about 90° C, though it rose more slowly. Emboldened by the success with the Vostro, I took apart the T500. (As an aside, it seemed like there were more parts to remove on the Vostro. In the end, it seemed easier to assemble. Some of the parts on the T500 took a bit of fiddling to get back into place. But... I was happy to find that both Dell and Lenovo provide detailed instructions on their web sites.) I was surprised to find no dust bunnies hiding in the T500. Lenovo seems to have designed air flow that reduces that problem. Neither was I sure that there was a contact issue with the heat sink. Nevertheless, I cleaned it up, applied some Artic Silver and put everything back together. It's been about a week I competed this work. I'm transcoding a DVD right now and CPU temp seems to have leveled off at 72° C. There was a benefit form repasting the CPU.

To summarize, this is what I saw on a Dell Vostro equipped with an Intel Core 2 Duo T7500 @2.20GHz
condition idle temp loaded temp
initial 47° C >93° C
clean and repaste 40° 80° C
undervolt 34° C 80° C

Lenovo Thinkpad T500 with Intel Core 2 Duo T9400 @2.53GHz
condition idle temp loaded temp
initial 47° C 90° C
clean and repaste 35° 72° C
undervolt 33° C 72° C

Testing was done at typical winter indoor temperature here - 68° F (20° C.)

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