Failed De dome diagnosis

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Joined: 12/24/2014 - 02:16
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Location: Ohio, USA
Failed De dome diagnosis

My curiosity got the best of me with all the talk about de-doming LEDs. Yesterday I operated on one of my sk68 clones, popped the circuit board out, pressed the heatsink and led out the front with a punch, and used a razor knife to carefully remove small slivers of dome off the top, until I got to a point where I didn't think I would be able to remove any more without exposing the LED. 

 

I carefully put everything back together just as it was with the plastic spacer between the aluminum heat sink and metal reflector. The first two or three times I switched it on the light worked, with a green/yellow ring around the hotspot pretty much filling what used to be the spill zone. I couldn't tell if it made any difference in throw so I walked outside, switched the light on, it came on and went out just as fast. Now if I look in the business end all I see is a tiny sliver of glowing light. 

 

I have used search but looking up "dim light" and "burnt out led" turns up a slew of other threads that have nothing to do with my issue. 

 

Any idea what went wrong?! Thanks!

pflexpro
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Joined: 12/26/2013 - 10:49
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Location: Georgia

I also de-dome by slicing. When you slice the dome use a very sharp razor. As you slice, you stress the lead wires and the bond of the dome material to the emitter…more slicing, more stress and a greater chance of failure. The dome material is bonded very well around the emitter, but not very well to the center phosphor. The key to making this method work is to keep the slicing to a minimum…use only one, diagonal sweeping slice using a washer as a spacer. The XPL is harder to de-dome using this method because there is less bonding area around the emitter and the dome tends to ‘pop off’ if you’re not careful.
It also helps to keep the emitter cold when slicing…I usually put my in the fridge before slicing.

So…one slice and a cold emitter

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So one (or more) of the lead wires are broken? Is there no fix for it?

pflexpro
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If it is a broken lead, the repair is very difficult. You should be able to see a damaged lead with a magnifier.

Sirius9
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Actually I think experts here recommend hot dedoming because when it is hot the dome is soft and easy to slice. Cold dome is pretty hard and you naturally tend to use sawing move (left-right) and that leaves nasty looking surface. Also when the dome is hot and soft there is much much less chance that you will damage the bonding wires. I use only gasoline method, and I only killed 2 emitters so far, and that was for testing purposes, I used old leds so no harm done.
BTW, if you damage those wires emitter is dead, no chance to repair them because they are so thin that, even with 25x magnification, smallest tip of your soldering iron looks huge comparing to those wires…

Dedomed XM-L2 emitter (notice the wires):

 

pflexpro
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When cold dedoming, I use a single diagonal slice that leaves a fairly smooth surface. It doesn’t really matter because the slice dedoming is followed by sanding and polishing (again both cold). The important thing is to find what works for you. I like the slice method because you don’t have to worry about sealing the emitter when finished.

…also, I didn’t want to say ‘repairing the lead wires is impossible’, because I’m sure someone has done it…just not me!