How to remove the XR-E from LiteFlux LF2X?

[EnabLED]

I have a LiteFlux LF2X where I'd like to replace the white Cree XR-E with a red Cree XR-C. I wonder if anybody who has had one apart can offer suggestions.

It looks on casual inspection like the XR-E is mounted on a "carrier" PCB with a couple wires from the "electronics" PCB. So maybe one approach is desolder the wires and pry up the carrier PCB, then reflow desolder ala kramer5150

http://www.candlepowerforums.com/vb/showthread.php?t=220008

Or...?

As to "why", I want to make a blinky light with a particular combination of size brightness, beam pattern, running time, etc. The programmable modes of the LiteFlux LF2 seem ideal, the regulator seems like it won't blow the red LED (~2.5 Vf), and for EDC I prefer my red-case Fenix L0D -- partly because I like the red case, and partly because I kept getting confused by the LF2's user interface!

 

[2xTrinity]

I have a LiteFlux LF2X where I'd like to replace the white Cree XR-E with a red Cree XR-C. I wonder if anybody who has had one apart can offer suggestions.

It looks on casual inspection like the XR-E is mounted on a "carrier" PCB with a couple wires from the "electronics" PCB. So maybe one approach is desolder the wires and pry up the carrier PCB, then reflow desolder ala kramer5150

http://www.candlepowerforums.com/vb/showthread.php?t=220008

Or...?

As to "why", I want to make a blinky light with a particular combination of size brightness, beam pattern, running time, etc. The programmable modes of the LiteFlux LF2 seem ideal, the regulator seems like it won't blow the red LED (~2.5 Vf), and for EDC I prefer my red-case Fenix L0D -- partly because I like the red case, and partly because I kept getting confused by the LF2's user interface!

I've actually swapped the LED in my LF2x for a Neutral White LED. There are two wire "bumps" that stick out above the PCB surface -- the LED is actually centered between these. These are actually connected to the positive and negative tabs on the PCB, you can determine polarity by running the light at low output, and probing these litttle "bumps" with a multimeter.

What I did was simply heat up the solder pads, and pry the old LED off. in one case, this actually lifted the copper trace on the PCB along with the LED. However, I was able to glue the LED to the heatsink with epoxy, then wire in the LEDs from above using 26gauge wire, soldered to those two bumps I mentioned.

Sorry I don't have pics hosted at the moment.

 

[EnabLED]

Thanks!

Did you try to heat both solder pads simultaneously, or one, pry, then the other? It sounds like I might benefit from heating both simultaneously to reduce the risk of lifting the trace.

Measuring the polarity before disassembly: good idea, thanks!

Out of curiousity, do you recall whether the thermal compound it came with is a grease type or an epoxy type? I'm trying to guess how much force I'll need to apply for removal.

Thanks again.

 

[2xTrinity]

Thanks!

Did you try to heat both solder pads simultaneously, or one, pry, then the other? It sounds like I might benefit from heating both simultaneously to reduce the risk of lifting the trace.

Measuring the polarity before disassembly: good idea, thanks!

Out of curiousity, do you recall whether the thermal compound it came with is a grease type or an epoxy type? I'm trying to guess how much force I'll need to apply for removal.

Thanks again.

I believe it was epoxy type, which means lifting the trace might be hard to avoid. I ended up using a dremel w/ wire brush to clean up the thermal pad. But it was only very sparingly applied to the portion underneath the thermal pad, NOT all over the whole device like a hand-made build would probably have.

The reason I soldered wires in from above -- rather than using the built-in traces was more the difficulty of not being able to reflow solder the LED. Gluing it down with epoxy, then wiring them from above is actually not too hard.

 

[EnabLED]

Thanks, that helps me plan the project. I'll probably try two soldering irons and try to figure out how to grab the existing LED more firmly. Good point also about using epoxy for the new LED.

Thanks again!

 

[EnabLED]

For anybody curious...

I tried heating the top side of the XR-E with no luck removing it.

Eventually, I switched strategies: I removed the LED PCB by alternately heating the poke-through wire on one side, then the other, lifting as I went. I was concerned this would desolder the wire where it goes in the electroncs PCB, but for whatever reason it was no problem. At least on my light the PCB uses thermal grease not thermal epoxy, so removal was straightforward.

I then desoldered the XRE from the PCB using a heat gun -- first run the heat gun until it gets up to temp, then put the backside of the PCB in the path of hot air. In contrast to the instructions for desoldering using a stove burner, there was no smoke, etc., so a heat gun seems like a good choice. (I was able to borrow one, but it looks like they are widely available for less than the price of an other NiteFlux LF2X.)

The LED PCB has a bunch of vias for the heat path. I thought it could be either that or a hole in the center of the PCB and a raised part of the case to reach the LED, which would have given a better thermal path. I cleaned the vias as best I could with acetone and a Q-tip to minimize contamination by the heat sink compound. I'm not sure whether it is a problem, but it seemed like better safe than sorry.

I lightly tinned all three contacts on the new LED, placed it on the PCB, then held it above the preheated heat gun to solder the LED to the PCB.

I applied a little bit of Arctic Silver thermal "grease" (one-part, not the 2-part epoxy). There was alread some on the case but it seemed like a good idea to replace what I cleaned off the LED PCB. There are three holes in the case -- two for the two wires plus a third one, I don't know what it does. The excess thermal compound did not squirt out the edges much, so probably some went down the holes towards the electronics. It should be mostly nonconductive but could change fine resistances of capacitance.

The PCB is held in place by two wires coming through small holes in the case. The thermal compound gets on the wires easily and the wires are easily bent but have little clearance to the case. So use care in reassembly.

I resoldered the PCB, "walking" it down the two wires by alternately heating with a soldering iron and pushing down gently. Once in place I added a little extra solder (not much!) to each wire to make up for what was lost in disassembly.

I've not stressed it, but have run it about 12h in a medium-intensity blinky mode. All seems good!