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David Robbins, K1TTT

K1TTT@arrl.net



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LED Bulb deconstruction

Less than a year ago I bought a CREE LED floodlight to try them out. Recently it had been flickering badly. I checked their warranty but couldn't find the sales receipt to send it back, so not having any other option I tore it apart. Sorry I didn't take more pictures, but you'll get the idea anyway I think.

Of course there was nothing showing that would give any hints on how to disassemble it the easiest way, so I attacked it from the bottom. First I removed the solder bead on the base, that was easy enough. Then I used a hacksaw blade to cut around the edge of the screw base where there was a series of crimps. This allowed easy removal of the screw base. Inside I could see the end of a circuit board and a bunch of rubbery grey potting compound. I picked away at the potting stuff till I could see that the board got bigger as it went in, so there had to be some other way to take it apart. I used wire cutters to nibble away at the plastic around the circuit board and eventually split it all the way down and found there were 3 plastic hooks holding it to the metal heat fin piece. Stick a screwdriver under it and pry a bit and off it pops. This is what I had at this point. The bulb, bottom up is on the left. Then half of the circuit board enclosure with the CREE name. Below that is the circuit board and then the screw base and the little ring that I cut off where it was crimped to the plastic. The grey stuff is the potting compound, kind of like a soft silicone rubber. Looking at it the assembly process for that part was to attach to metal base to the plastic, insert and solder the circuit board, then fill it up with the rubber stuff. It would then just pop on to the metal heat sink ring. Power would flow from the two big solder pads to two metal fingers in the bulb part. In this picture the two big capacitors on the back of the board have been bent up to look at the board.

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A slightly different view of the board, there are 2 inductors and another cap on this side. There is also a blue MOV and a surface mount fuse. In this picture one of the inductors and a silver mica capacitor have been bent up to look at the board better.

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The rest of the deconstruction went much quicker. I put the bulb assembly in a heavy plastic bag and hit it with a pair of pliers. After picking away the glass that was glued to the heat sink ring with a silicone caulk like material this is what is left.

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There are 10 LEDs mounted in a circle on a metal thing that just slips over the heat sink shaft, there are a couple plastic pieces that hold it loosely in place and an insert inside the shaft with two metal finger things that make the electrical contacts. These are the parts. The ring on the left holds the LED ring and the bigger spacer thing onto the shaft of the heat sink. The plastic piece with the 2 springy fingers is what passes power from the circuit board to the LEDs.

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The LED blocks on the ring are connected in series, and it appears that there are 8 individual LEDs in each of the blocks. The markings on the LED ring and the power supply board appear to point to the supply putting out 90V to run the LEDs. I tried lighting the blocks different ways and only got a flash as one of the burned out. I just didn't have the right combination of resistance and voltage to light one of the blocks at the right current.