I bought a set of Philips Hue White Personal Wireless Lighting LED Starter Kit on eBay which were listed as “untested” (just another way to say broken). These, when working, allow you to control the brightness of your lights via the internet from your phone. Being broken, I bought for a fraction of the cost. Now all I had to do was fix them.
This set comes with a Hue Bridge which connects to your WiFi and controls your light bulbs over ZigBee radio, and two white LED light bulbs. I knew that two of the three parts were probably fine and one was broken.
Both light bulbs lit to full brightness when plugged into a normal light fitting, however the Bridge did nothing when powered on – most likely the Bridge was the issue then. Time to take it apart.
The Bridge is held together by a clip and two screws underneath the foot pads, concealing a single circuit board.
The first thing to check is always power. The Bridge takes a 5V input, so the first question is “is the 5V rail supplying 5V?”. Measuring the voltage on my multimeter I quickly ascertained that, no, there is no voltage on the 5V rail. Measuring resistance, I also quickly confirmed that there was a short from the 5V rail to ground.
The new question is “where is the short?” This is often a tricky question because measuring resistance won’t help, because the resistance will be near to zero ohms everywhere. You can also give the board a good inspection to see if there are any damaged looking components. However, the most reliable method I know is to pump a large amount of current through the board.
Setting my power supply voltage limit to 5V and over current limit to 1A, I forced 1A through the shorted component. Quickly, a chip near the power supply got too hot to touch – obviously this component was shorting the power to ground.
Looking at the markings, I identified this chip as a TLV62565, a buck regulator. This makes sense being right next to the power jack – it must generate a lower voltage for the rest of the system. My main concern at this point was that the damaged buck regulator may have damaged something down stream if it wasn’t working correctly. Luckily, it only appeared to be generating about 100mV, so at least it wasn’t passing the full 5V. After removing this chip I confirmed that the short had disappeared.
I replaced the new chip and it works!
I don’t know what caused the damage. This chip is meant to have short circuit and thermal shutdown protection so it is unlikely to be damaged by anything it is delivering power to. My best guess is that at some point there was a voltage spike from the DC power supply which caused the chip to blow – not unlikely given that the chip is only rated to 5.5V input and the power brick feels cheap. Anyhow, now I have a working unit.