I’d say it’s most likely an FET failed.
FWIW, I’ve just pulled a 7880 driver out and taken a look at it. I think that it may be a flyback driver. I’m basing this on the fact that the inductor has 4 leads rather than 2. Flyback converter - Wikipedia
its difficult to know what failed first, as the glowing-red hot coil burned everything underneath it.
The torrid coil definitely has two windings on it, (four leads) i have used this light quite often with no problems. And have other lights with the same driver modded in it. I like the modes settings it has, regardless if its inefficient of not. Though it did have really good run times on the lower modes with the three NiMH cells in parallel.
Now you can rename it to PadmeFire 
+ 1
I had my 7880 running on single d cell and they burn as well.
Its probably a forced boost driver and they limit it to small single aa cells only.
its probably what happened here, with the three NiMH cells in parallel the current supplied might have been to high. I also use this same driver in single-AA lights with no problems at all.
Can someone link me to anything that explains the term “forced boost driver”? Thanks.
I’m not familiar with the term “Forced-Boost” driver either, as i known this 7880 as a Regulated standard boost type driver. ( steps the voltage up from 1.5 to the voltage needed to drive LEDs.
honestly I’m just blabbering words here but it gets to the point lol
I’m glad I didn’t use the word overclocked boost driver
facepalm
Oh but not all components fail open! Biggest reason I avoid tantalum caps. They are not only fond of exploding & shooting flames but also fail short.
This 7880 driver explosion is probably not due to tantalum. Though don’t know what under the coil.
I modded an old plastic incan billy light last year. The type that took a 6V lantern battery.
It's now running an XM-L and one of these drivers - powered by 8AA Eneloops in parallel for runtime.
The emitter is mounted on a PC chipset heatsink but the driver is simply sitting in place held by hot-glue.
I don't often run it at max, but perhaps I should do some spot checks on the driver temperature before leaving my latern unattended. Thanks for the warning DBSAR!
Do you mean to say the light was still working, until you turned it off?
Of course not! Fortunately only one needs to fail open. Or desolder itself, or whatever. Like I said, maybe I’m wrong… but that’s where my money would be: I would bet that the driver (as a unit) would fail open rather than build up enough pressure to pop the tailcap.
How much current is running to the LED on turbo? (and how much current draw from Battery) With rough estimate of driver (in)efficiency may be enough to glow a toroid.
Are you using the same 7880 Driver ?
I believe i discovered what happened in this case, the lead wires to the LED solder points are so close it loos like heat build up caused them to short together, meaning its not a fault in the driver. (Though it would be a good idea to check how hot yours is running considering eight Eneloops in parallel can send a lot of amps into a driver.
The specs stated 800ma, though i measured 1.02 A on fresh charged cells to the 219 on highest mode.
The LED went out when i heard the “pop” sound, then i noticed the glowing inductor coil and the flame from burning insulation and resin.
Good find DBSAR. That appears to jive with what I found previously with the efficiency dropping as input voltage went up. Maybe it’s more along the lines of efficiency dropping as boost ratio is reduced decreases. A dead short at 0.8A on the output would more than flip the ratio on it’s head.
Could just be a cold solder joint and with the leads being so close to each other, when it came loose, it just touched up against the other.