Repairing a LED energy saving bulb


I like energy saving bulbs, not just because they produce light more efficiently and, therefore cheaply, but also because they last longer, look funkier, run cooler and require changing less often.

Well, that's the theory. Unfortunately I seem to have been through a bit of a run of them lately causing me to take a closer look at how these things work.

My failed units are all from the same manufacturer and they haven't put in the distance so I won't be buying that brand again. I wouldn't mind if they were some cheap and nasty things bought off a nasty online auction site, but I purchased them from a reputable supplier and paid a premium price. I could probably get away with returning them as faulty however I'd rather take a peek inside to see how these things work and whether I can get away with my own repairs.

I'm looking today at an R50 LED bulb. This one is in green and is used for decorative purposes only (accent lighting around my aquarium). This particular model has fifteen LEDs and, no doubt, some clever bit of circuitry to convert the AC mains to a DC voltage to drive them. Surely there can't be that much to go wrong?

Only one way to find out. The thing is encased in quite thick glass....

Bulb before



Using gloves, goggles and a small hammer, the neck of the bulb is (delicately) chipped away to reveal those lovely innards...

Bulb with neck broken



Notice how the reflector has also cracked. This is important for later. Some extra chipping and biting (with pliers) allows us to remove enough glass to extract the driver circuit board.

The guts



We don't want to damage the reflector too much but for full disassembly we'll have to break it into two or three pieces along the cracks to remove the LED circuit board. So long as care is taken and it doesn't shatter completely it can probably be glued back together for reassembly later. With all the glass removed, we have access to all the components.

Upon tracing the connections on the circuit boards, I found this particular bulb has the following schematic...

Schematic



As you can see, there aren't that many components to go wrong. The resistor and fuse are the easiest things to check and my multimeter has a capacitance function so I was able to verify the caps were working correctly too. I wasn't sure how to check the bridge rectifier on mine (short of connecting it to the mains and checking the Voltage coming out of it) so I decided to check the individual LEDs next by connecting a 3V PSU to the connectors of each one to make sure it lights - and that is where I came across a failure. As the LEDs are all connected in series, if one fails it will stop them all lighting up.

The failed LED was removed - but what to put in it's place? I have a collection of LEDs but none quite the right colour (and most not even the right Voltage). In the end I wasn't able to match up a replacement LED so I fitted an ordinary diode salvaged off an old PCB onto the back of the board in place of where the LED had been. This diode should have the same characteristics as the LED it replaced except it doesn't light up.

Disassembled



Reassembly involved gluing the LED board back into the reflector which was itself glued back together. To give the bulb some rigidity and prevent exposure to live components, I used the plastic top off a Right Guard deodorant cannister which was exactly the right size for the job. A hole was cut into the plastic lid to allow the metal screw connector of the bulb to protrude while the open end of the lid was silicone sealed onto the reflector.

Bulb Rebuilt



Once inserted back into it's fitting, the casual observer would be unlikely to notice the difference between a rebuilt bulb and a normal one. The only real noticeable difference from the outside is that there is a missing LED - but would anyone notice (or care)....

Bulb repaired



... looks good to me!

This isn't the first time I've undertaken such a project either. Another LED bulb I have (a GU-10 cheap no-brand) failed after just a few days. I undertook the same method to get into the bulb where I found the cause of the problem to be a duff resistor. I replaced it with a spare and, at the time of writing eighteen months after the event, this bulb is still in operation.

I wonder how many of these things get thrown away because of a single faulty component?


Update
One year on and this thing is still going and getting weekly use. Another LED failed shortly after the article was written and it was 'repaired' again. Recently this green bulb has been retired in favour of a colour changing unit that Sainsburys were selling off cheap. Although this repair method works it's unlikely I'll bother with it again and when a similar white LED bulb failed I broke it up for spares as I needed some white LEDs for another project. The trick with these bulbs is not to buy the cheap shit ones in the first place and go for a reputable make. My failed bulbs were made my Pro-LIte while some more expensive bulbs made by Ring have been going strong for three years at the time of writing.