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Old 04-18-2011, 09:21 PM   #1
magnamark OP
What the?!!!
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Joined: Nov 2010
Location: Idaho
Oddometer: 2
How to fix your LED driving lights

The LED driving lights available online are all the same light. You can get them from
  • Sanjoh in the vendor forum
  • Komy Kwan(the cheapest place I've found them)

When one of these lights recently failed, I decided it might be more interesting to find out why they die, instead of sending it back under warranty.

After taking the light apart, I found that the thermal paste wasn't evenly applied under one of the LEDs. The slight burn marks along the edge indicate that it overheated and failed 'open', killing the entire light. The paste under the other two looked like peanut butter spread on bread with little care.

To fix - take the light apart. Info here: When you get down the heat sink, remove the three screws attaching the plastic lens. The LEDs are now free to slide around on the heat sink. Check to make sure the thermal paste is applied thinly and evenly under the entire heat sink. The application should be just enough to fill the voids created by the milling of the heat sink and the LED heat sink - in the thousands of an inch.

A quick check with a bench power supply confirmed that the other two were still working, by powering each independently.

I had a Cree XPG from ($13) sitting in a drawer. I unsoldered the bad one, soldered the good one, put a plastic washer on it to get the height to match the original LEDs.

Then, I spread out the thermal paste under all of the LEDs and reassembled the light.

The pictures show the light after replacing the LED. They're running at about 5ma, so you can see they're working. The other picture is back on the bike - I just shot it with my phone.

All in all, it was probably faster and cheaper than packaging them up and sending them back to the vendor. Now, if I could just find the exact replacement!

Added photo of repaired light running full power. The single LED centers nicely.
Shot in full daylight f38 : 1/2000.

The black ring is a plastic spacer added to match the height of the stock LEDs. The silicon looking ring around the edge is just that. Unfortunately on my final assembly, the glass slipped out and it broke. To silicon is there to seal the edge until I get a glass replacement.

Happy tinkering.

magnamark screwed with this post 04-20-2011 at 07:37 AM
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