Wednesday, July 20, 2011

Repairing LED Lamps Part 2


More Bits of a LED Bulb
Part 2 in the 
Repairing LED Bulbs Series

What you are looking at in the above photo is a close up of a "star" or mounting disc for the LED diodes. You can see on the top right where I removed a faulty LED diode. You can see also where I have started to scrape away the old thermal paste from the mounting area . The old paste comes away quite easily by gently scraping with the tip of a small penknife.

I have un-soldered the power leads which come up through the square hole in the middle, and I have clearly marked the contacts in pencil with the  + and - so I don't get them wrong when I re-solder. The reason I have un-soldered the "star" input leads is twofold, one is so I  can check the driver circuit, and two is it allows me to work on the star more effectively.

The above picture shows the heatsink. It is really quite a pretty piece of aluminium. It's sole purpose is to radiate away the heat generated by the LED diodes. The same type of heatsink moulding is used in both the GU10 and MR16 bulbs. The base has regular screw threading but the outer rim has a threading but into the leading edges of the fins.

There - you have a good view of the threads on the fin edges. This is where the ring that retains the main lens is screwed onto. It is very important not to cross-thread these guys - needless to say! It is also important that the retaining ring is fully tightened, as this presses the lens against the star, and in turn presses that star against the flange of the heatsink. If the lens retaining ring gets loose, the star will not have good thermal conduction to the heatsink - and the LEDs will either blow or go off colour and dim.

What you are looking at in the above photo is the base of a GU10 lamp with the driver circuit, which is usually pushed down into the tube, pulled out for inspection.

And here is the driver circuit board with it's little transformer and capacitors visible. The red and black leads are the positive and negative DC voltage going to the LED diodes.

That's it for this post. Keep a look out for more posts in this series. They may not be posted in one chain but are more likely to be interspersed with other material. Also, I am waiting for some spare parts to arrive from the Far East, and this might delay the series a bit.


No comments: