Repairing an LED light bulb

One of my beloved power saving LED light “bulbs” suddenly stopped working, far before it had reached the end of it’s promised and assumed 50.000 hrs lifetime.

A good occasion to dissect the poor device and to try to repair it, or at least: trying to understand how it works!

The dissassebled "Lightbulb"

While the LEDs were accessible by removing some screws and could be verified to be ok with the diode testing function of a cheap DVM (they lit up slightly), it was a bit tricky to access the actual electronics (in the socket, the device that is converting mains AC to about 9.5 Volts of DC (measured) – the LEDs are in series). I finally was successful with a drill (see picture), making holes into the socket pins at 2 positions each: First, in order to sever the wires to the PCB to get it out and also to create new holes to enable the rewiring with new leads later.

The extracted power supply

The extracted power supply

Some basic tests (signs of burn, fuses, rectifier, diodes) did not reveal any faults. Interestingly, when connecting the opened device to AC (actually, to perform some in situ checks), and after I started worrying about obtaining an MJE13003 in a TO-251 case (TO-220 is too big, TO-126 might not fit, too) or an AP3706 for a reasonable price), the light simply worked as nothing had happeed. Seems, the problem was a bad “mechanical” connection of one of the wires at the socket. Added some new wires to connect to the socket and reassembled the whole thing.

Now I am enjoying my resurrected light bulb and am happy about having saved some money and prevented  premature electronic waste.  Although in terms of economics, it was not “reasonable”, the whole project took me several hours. But it’s one of the things you can do to lift up your spirits while you’re waiting for your work permit being processed :).

View on the AP3706

View on the AP3706

Some background: The whole circuit is constructed around an AP3706 controller (3rd picture), a driver for switching power supplies. For a prinicipal schematic, see the application note e.g. here: http://www.diodes.com/_files/products_appnote_pdfs/power/sw_reg/AN1028.pdf. Not many things that actually can break down: A 1A fuse, the AP3706, a MJE 13003 NPN power  transistor and 2 diodes. In any case, it might be worth not to discard such a device, just because it has stopped emitting light.

For soldering on the LED plate and on the sockets, you’ll need a high power soldering gun (mine has 1kW) or something similar. A standard 50W soldering iron won’t work, due to the high heat capacity of the aluminium (cooling) plate that holds the LEDs and of the socket contacts. However, to fix the new leads at the green PCB, a standard iron is the better choice.

Although it won’t make much sense to buy replacement electronic parts as you’ll spend almost as much as a new light bulb will cost you, it should make sense to keep “burnt” ones and use theirs parts as spares.

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One Response to Repairing an LED light bulb

  1. Herb says:

    Good job, well done. Please consider the ONE part which often fail prematurely: It´s the electrolyte capacitor. When losing its capacity, the entire circuit may work instable. I recommend to have a conscientious look on such parts. At least it should be a type marked with “105°C” and providing a low ESR.

    all the best, Herb

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