Teardown: What killed this LED bulb?

-September 20, 2016

Last time (I think) that EDN took apart LED light bulbs was the spring of 2011. The market's matured quite a bit since then, and the technology's gone mainstream in a big way, thanks in no small part to plummeting prices. Look, for example, at a couple of current case studies that I collected in the process of developing this writeup:


A while back, we hung two ceiling-mount lights in my wife's office, each containing two 60W-equivalent dimmable A19s from Home Depot. Speaking of dim, however, the daylight hours are getting shorter post-solstice, and she therefore recently mentioned to me that she noticed the office was dimmer when artificially illuminated than she'd previously remembered it being. I found that one of the two A19s in each light cluster had mysteriously failed; for now, I've replaced them with (non-dimmable, since the wall switch is actually conventional) CFLs that I had on hand. And of course, I'm "making lemonade out of lemons" by taking one of them apart to see what's inside (and what might have failed).

Here's an overview shot, to start:



Along with closeups of the various exterior markings:





The metal base is screwed into the plastic base below it, then crimped to hold it in place:



Had I been even mildly intelligent about this project, I would have closely read Margery's past coverage before proceeding with the dissection, versus afterwards. Had I done so, I might have gotten the clue to put the light bulb in the oven in order to loosen the glue holding the globe and base together. Instead, I went at the seam with a box cutter, followed by a screwdriver, with the desired end result, mind you, and only mild casualties.




Here's the LED array I found inside, absent any discrete diffuser in front like the one this guy found:



And here's a marking closeup:


Click to enlarge.

Prying the LED plate away was straightforward, thanks to the aforementioned screwdriver:



But getting underneath the underlying metal "cap" wasn't as easy. It press-fit to the surrounding metal chassis, but working around the edge was ineffective:



Instead, after snipping the two wires that powered the LED array, I stuck the screwdriver in the center hole and pried it away that way:


Here are two views of the still-glue-installed PCB I found inside:




A pair of pliers enabled me to remove the metal base with relative ease (and no more injuries):


That exposed the PCB bottom edge; as this same-as-before guy found, the exposed wires are contact-compressed to the base, not soldered to it, simplifying the assembly process (at the tradeoff of an incremental potential-failure point):



Pushing out the PCB was then straightforward:



Here are top- and bottom-side PCB closeups of the various AC-to-DC conversion and other analog-and-power circuits:


Click to enlarge.


Click to enlarge.

Any guesses on the failure root cause, readers?


Also see:

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