Butchering an LED bulb

  • December 6, 2018
Categories
Mucking About With Things The Diary of Lupin Pooter
Flickering LED bulb boasting a urine-stain-yellow ring of death.
This light bulb (Philips 18W 6500K 2000lm 150mA 220-240V ac 50/60Hz 9290011650A) had the temerity to flicker, so it got to taste the cold HSS of my hacksaw blade.

When one of the bulbs in our kitchen began to flicker, I saw a chance to sate my curiosity as to what was inside.

Markings on the base of this bulb.
The meanings of the first two lines’ worth of markings on the bulb are self-evident.

After “Made in China”, the glyph that resembles the head of a trident (or maybe half of a Greek letter theta turned on its side) is a factory mark. It would tell someone in the know precisely which facility in China produced the bulb. Alas, the Strictly confidential! Philips Factory Marks document available as a PDF via the Factory Identification Symbols link on the LAMPTECH Lamp Markings page was last updated in 1986. Thanks to a different PDF file hosted by the same site, I know that the first two characters in the string 5DH indicate that the bulb was manufactured in April 2015. The significance of the H is, to me, unknown.

photo of the bulb with the globe sawn off.
The plastic globe was easily removed.

Some hacksawing got the globe off. Unfortunately,it didn’t occur to me to snap a straight-on photo of the LED array until after I’d pressed it face-down against my bench top and spent a few minutes enthusiastically sawing on the base, closer to where the screw-threaded connector was attached.

The bulb contained twenty-three SMD LEDs.
Now I know that the yellow phosphor coating on an SMD LED is very brittle.

As you can see, more than half of the twenty-three LEDs inside the bulb have been visibly damaged, losing their yellow phosphor layers. Oops.

Notice the orientation of the wires from the PCB.
One of these wires (guess which) was joined to the metal pin at the bottom of the connector and the other was bent back up the inside to make contact with the inside of the screw-threaded bit.

Getting the screw-threaded socket connector off was simply a matter of twisting and squeezing. With that done, the PCB was visible, but it wouldn’t come out. The board-to-board connection to the LED array was via 2-pins which slid surprisingly loosey-goosey into a pair of what looked a lot like female crimp-on “DuPont pin” connectors. They’re visible sticking straight up and out through two of the center of the LED array in the preceding photo.

Done.
The original, plain old HSS blade would probably have gotten the job done, but I swapped it out for a blade that supposedly contained 8% cobalt.

At this point, having used pliers to snap off all of the bits of the bulb base that consisted purely of plastic, I realized that, beneath the remainder, was a one-piece shell of aluminum. Switching blades to one intended for cutting metal and exercising what I thought would be sufficient caution, I cut away enough aluminum to remove the PCB.

This side has through-hole components.
On this side of the PCB, you can see some capacitors, a transformer, and an inductor.
Done.
On the other side of the PDB, it’s all surface-mount stuff.

See how I managed to saw through one or more traces on the surface-mount side? That put paid to any thought I might have had of trying to diagnose the cause of the flicker. Maybe next time.