I got a Roche F12 a couple weeks ago. I have been running it on high alot. Recently it went from 3 modes to 5 on its own. Today it went dim in all modes. Could the driver be messed up? I am trying to figure out how to remove it but haven’t yet. Any suggestions? Thanks.
First some diagnostics: This light suffers from the tube being too small, both length and width - what type of batteries are you running in it?
Running @ HI alot —> too much heat —> problems with soldering? 
One of your issues is probably a bad solder connection on the star that sets the driver to 3 modes.
Check the underside of the driver board, one of the stars should have a solder blob on it that connects the star with the outer ring.
I am using an unprotected Panasonic 2250 mah IMR battery. It went from 3 to 5 modes when I put a protected Eagletac 3100mah battery in it. It stays in 5 mode regardless of battery. I really don’t mind the modes. It is the dimmness I want to fix. There is a blob of solder on the 3rd star that contacts the ground ring.
Even though the solder blob looks ok, it might have lost its electrical connection.
My guess is the battery you put in was a tad too long, and the resulting pressure on the driver board cracked some solder joints.
You could try and measure the tailcap current with a DMM, if it can be divided by 350 mA, you can calculate how many of the 7135 chips are still working.
I think Steve is on the right track. My shortest cells are TF 3000 Flames and they just barely fit. Even so, they have squished the spring on the driver board. If I were to use a longer cell like an XTAR and forced it in, it would cause some damage.
Thank you for all your responses. I went ahead and sacrificed the driver to find out how it comes out. The brass ring is pressed in to hold the driver in place. Carefully pry it out. I plan on replacing the driver soon.
I went and made a mess of adding more 7135’s and had to dremmel out the retaining ring, and wondered how much nicer it would have been if it was threaded instead of pressed. Good luck with yours.
Mine went from 3 to 5 mode also last summer. Works fine on 5 mode.