For those curious about what is inside of the Rovio TrueTrack beacon, and for those who are having problems, here's the inside scoop.

How To Hack Open The Rovio TrueTrack Beacon

Removing the beacon 'eyeball' from a dock or a room beacon is pretty simple- all you need is a medium phillips head screwdriver, and a 1.5 mm hex key to open the eyeball. 

• Remove the mast- squeeze the plastic tabs on the bottom together to unlock, and wiggle the mast out.
• Remove the 6 screws from the underside of the base. Set them aside with the baseplate so they won't get mixed up with the others to come. 
• Remove 2 screws from heat-sink and 3 screws from the circuit board.
• Remove 3 screws holding the beacon base to the dock.
• Remove 3 screws on the beacon retaining ring.
• Now you can use the hex wrench to remove the one screw holding the eyeball halves together, on the side where the power wires come out.

This is the inside works of a 50 Hz room beacon. You can see the 4 small screws that hold the lens assembly on. At the bottom, R42 is present next to J3 marked "50 Hz": you can convert this beacon to a 60 Hz simply by removing R42. The labeled thru-holes on the right (CEB, GND, SDA etc) are not present on all versions of the beacon. At the top, to either side of the largish capacitors, are the three pins of the output transistors that drive the IR LEDs. Jump down to see the other side!

This is the LED side, that is normally covered by the lens assembly. At the top are two transistors, marked 'C2328A' on this particular beacon. This matches the part number for a 1W  NPN power transistor in a TO-92L package. From this view, the pins (left to right) are Emitter, Collector, Base. The IR LED is connected between the collector +5V, so the transistor is sinking the current to ground.

Repairing the Rovio TrueTrack Beacon

If your Rovio starts reporting 'Low Nav Signal' even when docked or under the beacon spots, it's time to check the IR LEDs. If you have a digital camera, try aiming it directly into the beacon lens- you should be able to see two bright spots if everything is OK. If you only see one, or no bright spots at all, it's time to open your beacon. [Caution: it is easy to damage other components on the beacon when probing - 

Diagnosis

There are several reasons why your IR LED may not be working. Before buying anything, check the following to determine the cause. Then proceed to the appropriate repair section below for further instructions.

1. The LED itself may be burned out. Use a voltmeter to check the voltage across the LED. A good LED will show about a 1.5V. If the LED is dead, you'll see about 4V, because no current can get through the LED.
2. If the LED is good, feel the transistors: if one (or both) are very hot (too hot to touch)- unplug the beacon! Your problem may be in the tiny surface mount package marked 'Q1' on the other side of the board. Q1 is a dual-NPN transistor package, and if defective, can be replaced with a pair of any small-signal NPN transistor such as 2N2222A. 
3. If the transistor is cold, it may possibly be burned out. Examine it closely for damage and give it the sniff-test.

1. Replace LED

Acquire replacement IR LED(s). Look for 940 nm output wavelength, narrow angle LEDs with ~1.5V forward voltage. Radio Shack 276-143 will work; in the UK, RoboCommunity member Hubba found that Maplins code number YH70M also worked. To prevent burn-out of your new IR LEDs, also acquire some 10 ohm 1/4W resistors (recommended for 100mA LEDs). [since the beacon is flashing at 50% duty cycle, current of up to 200mA should be safe. The voltage drop from the LED to ground is about 2.5V and there is already 1.8 ohms resistance, so 2.5V/(10 + 1.8 ohms) ~= 212 mA]

You may need to adjust for a different beacon board layout, but in all cases the center terminal of the output transistor is connected to the (-) side of the LED (commonly the short lead), and the (+) side of the LED is connected to VCC. Bend the leads of your resistor and LED as indicated below, trimming the lengths to match your board layout. Solder the leads to the terminals as shown here.

Here's my board after attaching the new LED. I should have trimmed the side of the new LED a bit so as not to obscure the red LED, but it still works! My nav signal (using http://X.X.X.X/rev.cg?Cmd=nav&action=1 where X.X.X.X is replaced by Rovio's IP address) is now around 11,000 when under the beacon spots.

Here's the red beacon pattern now:

 If you have discrete LEDs on your beacon board, carefully unsolder the defective LED and lift it off (as demonstrated by Nocturnal below). Bend the leads of your LED to match the pads, keeping them short so the LED will sit low to the board.

You should now test the beacon with Rovio and confirm that both IR LEDs are working and that Rovio is detecting a good Nav signal now. You can also use your camera to verify that both IR LEDs are now lit.

Nocturnal graciously photographed the output of his repaired beacon, verifying that these LEDs can cast a usable beacon signal!

2. Replace Q1

This will be the focus of a future article.

3. Replace the output transistor

This will be the focus of a future article if warranted (I haven't found any to be burned out or in need of replacement yet!)

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