I popped a Mtn 17DDm driver today. The reflector on one of my lights got to close to the LED wires… 
It appears that I have a direct short now across the input of the driver. I see not physical damage. I am making the assumption that the FET is toast, is that a fair assumption? I will venture into replacing it this weekend. Do any of the other components usually get toasted when this happens?
Matt
Any modes work at all?
Not a FET+1, and it appears that I have a direct short on the battery side. 0ish ohms and my bench power supply goes into current limit on contact.
Could it be the MCU?
This isn’t really my forte, but I’m interested in finding the problem.
I have an original BLF 17 DD that I blew up by soldering the zener on backwards and running it with two cells in series. I’ve been wondering if I can get it working by replacing the MCU with one taken off a Qlite.
Please post you’re results, as I am constantly causing bad things to happen to drivers.
Have you taken the led out of circuit? Once a long time ago I had a led fail and short. I remember thinking how the heck? Wouldn’t it go open like an incandescent bulb? Turns out they can do both but shorting is more common.
When I pop the FET I can smell it, and usually see its gut’s bleeding out, some glossy liquid sticky melted stuff? I keep a healthy stash of all (3) LFPAK33, LFPAK56, PowerPAK SO-8. And I pop quite a few and It’s usually just the FET, Easy enough to replace. 
Just don’t get it too HOT when doing it!
The LED is ok, tested that first. I have already installed a new driver in the light and all works as it should. The top of the fet looks like it has black magic marker on it, as does the MCU. Under magnification I do not see any physical damage to any of the components. With a DMM, I checked the FET in circuit and from S to D to G I have almost no resistance on any of the combinations. By almost the most I can find is about 3 ohms. It seems to me that a DMM should not supply enough current to power the FET, so… I think it is blown. It looks like a part number of 1508n? It is a LFPAK56 MOSFET, based on form factor. I hope to replace it this weekend, I will use hot air… I am not steady enought to do it with an iron.
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Good luck. Hot air swap should take about 15 seconds.
The little 7135 under the wires was hidden from my view, so yes it was a FET+1. The FET was blown, replaced it and all is good with the driver. I belongs in a UF-2200 and has been restored to it’s home… I love the light, but I am struggling with the tail switch in this light. It has a plunger and nylon spacer on top of the spring. I had to replace the spring when I got it, the old one had been melted. I also replaced the switch at the same time. I have to back off the tail cap about 1/16th of a turn for the light to turn on reliably. I added a little solder around the lip of the switch board and that helped but did not fix it. I think I need a slightly thicker switch board and almost a long 105C type of spring to work properly… But, the old girl is back to 4.9 amps at the tail and I have my ML mode back!
One should really not work on drivers late at night after taking cold medicine!
Matt