Sunday, January 31, 2010

Next up, the Slingbox Pro-HD

I just purchased a Slingbox Pro-HD from a local Best Buy. In case you dont' know, this cute little device let's you turn either a video source or your CATV/Hi Def TV Antenna into a network resource.

Once plugged in and configured correctly it let's you watch your video sources (think Cable or Satellite box) from anywhere in the house or even around the world in HD assuming you have the bandwidth for it.

Unlike a lot of network appliances out which had completely inadequate cooling, the Slingbox has pretty good cooling thanks to the perforated panels on the front and back, along with vents under the feet which have enough spacing to actually allow air to get around the circuit board and up into the appliance. I thought I wouldn't have any issues with it, but after using it for a couple of days I noticed two things. First, that occasionally I'd have to power cycle the Slingbox to get it to work, and secondly that the underside of the box gets wickedly hot. Not only does this bode ill for the chips inside, it also means it's giving my DirecTV receiver excess heat. Time for a little investigation!

First, had to figure out how to disassemble the box. There are four screws which hold the entire thing in place, cleverly hidden underneath the rubber foot pads. Easy to do. You also have to take off the cosmetic metalic perforated grill on the back. It's no big loss to toss it. No one's ever going to see it and it just gets in the way of air flow. If you are careful though, i'm sure you can put it back on.

Four screws hold on the metalic shroud which seems to be to contain the EMI/RFI coming out of the box. Once you've taken that apart, you'll see something like this:

Overall a nice layout, but not a single heat sink in site. The good news is that Slingbox seems to have taken the high road, specifying higher temperature grade parts than they could have gotten away with, especially that TI chip in the middle.

That is a combination RISC/ARM chip and DSP designed specifically for video processing. At idle it reaches about 100F, but when transmitting video to your PC it runs at about 150F, or close to 85C, the upper limit of the standard issue chip. The temperature underneath that chip seems to be about 10-15 colder. So you can see why cooling this chip would be good for the Slingbox and anything beneath it. You may also notice big copper areas underneath the MOSFET devices. These are used to cool off the MOSFETS by transfering as much of the heat to the circuit board itself.

Something else I noticed. This box is never off. All the major IC's stay hot even when it's not doing anything. The coolest the TI chip ever got was around 100 degrees. As a result, I've decided to start off by adding some passive cooling. Using a combination of new Zalman RAM heatsinks and an old 80386 heat sink I took a first pass at cooling this beastie down. Below are the results.

That round black heatsink is probably complete overkill, but I will say that it's temperature now is about 30 degrees cooler than it was, and that the underside is cooler as well. You may also want to substitute the Swiftech VGA RAM coolers instead of the Zalman. They're copper, and about twice as tall which may give you a little better performance.

I'm not sure either solution alone satisfies me yet, and I have found an extra power supply. The generous people over at Slingbox have included a USB port on the back of the slingbox, for which I have no use for, except to attach a small 5V fan to! Muahahahahah. So, the next part of this project is to take a fan that originally went to a hard disk cooler, and attach it to the underside of the top panel, and power it through the USB port. If I can do that I know I can bring the CPU temp down from 120 to about 100 or less.