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LED light repair

davidsrsb

davidsrsb

pfm Member
Not HiFi, but a useful tip.
One of four LED downlights in my kitchen suddenly went dim and flickering.
It is about four years old. Changing one would have been hard to match appearance and brightness.
Opened up the dc controller box and I took out the two electrolytics.
Output is a 100uF/35V and measured 98uF
Input rectifier had a 6.8uF/400V, measuring 0.0uF
I changed to a much bigger 10uF/450V (and replaced the other cap too)
All working nicely, just slightly brighter than the other three lights - they must be going too.
Cost 30p. :)
 
Electrolytics in lighting equipment often have a very hard life - I have replaced caps in a bedside touch lamp twice in less than fifteen years, there is very little space to fit anything better than the original type, you are wise to fit bigger better caps when you can.
 
These looked a bit small - 6.8uF is an unusual value and probably chosen to be 1c cheaper than a 10uF.
My kitchen lights are on for several hours a day and the temperature at ceiling height is almost 40C
 
Further to this a second light suddenly went dim, so I changed the capacitor and the other two lights.
An interesting experiment.
The capacitor was a 8mm diameter 6.8uF 400V 105C
Two failed to zero capacitance., both had seal failure.
One looked healthy and measured 7.2uF
One had seal failure, but still measured 7.0 uF

My conclusion is that the seal goes, the electrolyte dries out and then the capacitance drops very suddenly at the end. Capaitance changes too late to be a useful early warning
A pity that I cannot check the ESR.
This was after 4 years service.
 
Also true of CFL bulbs. They fit the cheapest nastiest Chinese electrolytics only just up to the job even when new. I reckon this is the designed in failure mode to make sure they don't last for 15 years and so give the industry a turnover...
 
CFLs are hard to service, the LED lights usually have a separate power supply, which is easy to open and investigate.
 
The bit I hate is getting them out of plasterboard without damaging the hole with the spring clips.
 
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