Reverse Engineering

The industrial design of a TV is really interesting.

I got a chance to disassemble and reassemble an HDTV at work the other day (with some reason). It was a fun afternoon. Disassembly time: unclocked; Reassembly time: 38mins. No screws lost, no extra parts leftover.



I wrangled my way into getting a full technician's tool kit when they hired me, but the project only required a hex wrench and a Philips-head screwdriver.



When you take off the back plastic cover, there's an internal metal chassis. Good TVs have substantial internal shielding because of the FCC's electromagnetic interference (EMI) regulations. EMI happens when there is a voltage transition on a wire (ie, power or data). That transition has a corresponding current pulse, which produces a magnetic pulse that radiates outward. Hence, electro-magnetic radiation. EMI worsens when your voltage swings are large and fast. The larger the voltage transition, the more current you need to make it, the larger the magnetic pulse and the greater the EMI. The faster the voltage transition, the more current you need to make it, the larger the magnetic pulse and the greater the EMI.

The source of the EMI inside a TV is typically from the power supply (if it's a switching supply), unshielded internal cabling and poorly-laid out printed circuit boards (PCBs). Things like proper shielding, short cables, current-balanced signaling (low-voltage differential signaling, like that used in HDMI, or differential current mode logic), and proper terminations improve system EMI performance. However, high-volume manufacturers are cheap and won't use a multi-layer PCB with ground planes when a 1-layer board with jumpers will do. So, they ultimately have to make up for the cheap components with the expensive metal chassis a.k.a. Faraday cage.

Not only do cheap TVs without shielding violate FCC standards, they also tend to have weird artifacts when the EMI from one part of the TV (say, the power supply) couples into another circuit (like the receiver) and introduces noise and offset into the signal path. This TV is build really well, though. The more sensitive high-speed digital circuitry is well-protected.



On the right in the picture way-back is the power supply and the high-voltage circuitry for driving the LCD. That's built on a single-layer board with all through-hole components and pretty huge electrolytic capacitors. That design method's been in play since the 1970s. The receiver board and input circuitry is on the left under a shield that screws to the main chassis - we know that because that's where the HDMI and cable inputs are.



Under the first shield is a second shield with a built-in heat-sink for the main video processor. Please note the secret to high-speed disassembly and reassembly: mark the various screw mountings with flag tape as you remove the screws. This is useful because manufacturers cut every corner possible, so you can't trust the assembly markings. The case (and the board) are over-designed, so the manufacturer will strip the actual number of components down to the bare minimum in order to get better profit margins. Some overseas low-cost, high-volume manufacturers are even known to take a PCB design and start removing components until the design fails -- then they put the last component removed back on. Bam! Instant cost-reduction. For this TV, you can see that all of the cabling is unshielded ribbon cable or unshielded 30AWG stranded cable and they aren't using any ferrite chokes (ie, that lump on your monitor cable that also helps improve EMI). But, like I said earlier, their metal chassis makes up for that, and, hey, the low-profile PCB connectors are nice.



I couldn't remove the heat-sink entirely due to some permanent plastic rivets, but I got it up enough to fully expose the receiver boards. There are two: one for all the digital functionality and another, (only part of it is shown) that handles all of the analog inputs and audio out. The first photo is of the digital inputs with the main processor/scalar. The second photo shows the cable tuner on the digital daughter board (in yet another shielded enclosure). The analog daughter board isn't shown, but it's the darker green board you see connected with the 3 flexible headers.



Then I did what I needed to do inside the TV, put it back together, and it still worked! The. End.

As Hard As I Can

Well, it's 1-31-2007, the first anniversary of the Ignignokt scare, and once again, I'm spending this time in NC. My prototype demo was completely unscrutinized by Logan security. I have heard (so far), "Wow, that's big!" and, "It's so complex..." It's mostly just a kludge.



Of course, it's got enough parts that it didn't really survive transit all that well. It worked before I packed it up on Tuesday night. Now, after two days, the hardware appears to work, but the FPGA is talking smack to its surrounding circuitry instead of the smooth and rhythmic cadence of jive. Oh, poor broken thing... bless it's heart.

I'll be here working over the weekend.

Also, if you have to change flights on US Airways, and the new flight happens to be cheaper, you will not get a travel voucher for the remaining difference. Which is lame, considering they'll charge you the full $130 change fee, regardless.

Unscrewed

I didn't make this titanium screw. What I did do, is I carried it around in my shoulder for four months. I feel like that must count for something.

Happy Halloween

(1 x red LED + 2 x AA batteries + 100 ohms + wire + electrical tape) = fuse.



Spy vs. Spy - the game is on.

Korean Stir-Fry

My friend's mother is always sending her very good Korean food - all prepared and ready to defrost and eat. Unfortunately, we depleted her supplies rather quickly, so adventures in cooking were required:

Korean Beef/Thai Stir-fry

1. Take thinly-sliced sirloin and make a spicy Korean beef marinade: sesame oil, soy sauce, chili peppers (jalapeno or habanero + some seeds), sugar

2. Lightly fry generous amounts of minced garlic and ginger in sesame oil: add beef.

3. While the meat is browning, make up your sauce: sesame oil, peanut butter, tamarind paste, soy sauce, lime juice, siracha or red pepper to taste

4. Add chopped onions to the browned meat; saute; add your sauce.

5. Add green onions or sundry other vegetables.

6. Serve over a bed of rice noodles or vermicelli with spinach, cilantro, mint, sriracha sauce (rooster sauce), lime and peanuts (or any combination thereof; including other raw vegetables). Goes well with beer.

Grrl Power

I have successfully planned and installed my first floor (in less than a weekend, even). The mission: to upgrade Laura's unfinished office in the Broadway warehouse from bare concrete with traces of carpet adhesive to a vinyl tile floor.

On Saturday, I took stock of 'how to' sites on the Internet, picked up Laura. We went to Home Depot armed only with my engineer's computation pad and determination and a rough estimate of the room's dimensions from Matt's schematics. To the flooring section! We picked out tile (and designed the floor pattern), estimated minimum and necessary placement of 4'x8' sheets for the underlayment, got nails and cartridges for the Remington powder-driven nailgun and other sundries. After checking out, it turns out that our eyes were too big for my Honda Civic, so it was back into the Despot for carpet pad, clothesline and a razor knife (John from Flooring earnestly made sure we had the right trowel and then excitedly showed me his fool-proof trick for cutting edge tiles to size).

Laura and I then strapped the 4'x8' sheets of luon (ideally, you'd use plywood, and this is one of the corners we cut) to the roof of my Civic with the clothesline (with some doubtful and informative comments by a grizzled old contractor). It was secure, but still... I've never been happier to hit traffic than I was when we had to get onto Storrow Drive West to go to Back Bay. A cabbie yelled that we should have used 2x4's to keep the boards flat and a cute blond girl in a fast red car looked at our plywood and our wee little Civic and smiled at us while we were stuck together in traffic. We arrived without incident and unloaded and got to work.

Step 1: cut the underlayment and piece it together. Step 2: fun with powder actuated nailguns! It turns out that power level 3 is not quite enough to put 1" nails into concrete, but hammers can solve this particular problem. Step 3: "stitch" along the underlayment seams with a staple gun. Pound flat. Step 4: mark center lines and dry lay tile. That's where we stopped for Saturday. Sunday morning, we pulled up the tile in quadrants, spread adhesive and then glued the tile down as such:

 Step 5. Iterate. And once we were done, it looked like this:

If you look carefully, you may notice that it's an interwoven checkerboard of vertical gray and vertical white crossed by horizontal tan and horizontal white. If the tiles came with serial numbers, we probably would have had a hard time not laying them in serial order. But, hey. Floor!