BLF member Bequerelio posted a link in another thread to forolinternas.com where they discovered that a UF-2100 can be converted to 5-modes. The pics didn't really show well what was done and the conversion from Spanish to English doesn't help much either. I decided to try it and it is still amazingly easy. I wasn't able to take pics while I did mine but it is easier to just describe what needs to be done.
To do the mod you need needle nose pliers (to remove the pill from the head), a soldering iron, and desoldering braid or solder sucker.
Unscrew the flashlight head from the body.
Unscrew the pill from the head.
Remove brass retaining ring from the rear of pill exposing the driver PCB.
Pull driver free from pill to expose the internal side of PCB without damaging the wires.
The IC chip is the larger chip on the board and has eight legs, four on each side. One side will be at the outer edge of the PCB. This is the side we will work on.
Looking at the four legs at the edge of the PCB you will see that the 2nd leg from the right will have a solder bridge connecting that leg to the outter ring of the PCB. Warm up your soldering iron then, using your desoldering braid, or solder sucker, remove the solder bridge but be sure not to desolder the chip leg to it's mounting point.
With the soldering bridge removed, put the PCB back into position and press the brass ring securely back ino position making sure you have it tight against the PCB.
Replace the pill back into the head and reassemble the light.
I can’t take amp measurements but I compared it to my 3A driven jaws light before I did the mod and it’s still the same brightness after the mod so I don’t see any difference in output at all. It’s still bright as hell.
I suppose if you did see a difference you could just solder the bridge back and go back to where it was at 3-modes. I don't see any difference in mine.
Thanks for adding the pics and tail cap measurements, Heke! It's truly an awesome mod and if anyone who has a 5-mode would be willing to look, I'm betting they can be converted to 3-mode (not that they'd want to). Definitely no need to pay more for the 5-mode as they are likely the same exact product.
Flat side goes against driver. I use a pair of smooth jawed slip-joint pliers to press the ring in place working my way around the pill a litle at a time until fully seated. Don’t press the ring fully from one spot or you will distort the ring. Think of it like tightening a head gasket or wheel on your car. If not tight against the driver it will not work reliably or at all.
I used the tip of a small pocket knife and worked in under enough to get a small gap. I then used a small screwdriver and twisted and poppedy it off. It’s not easy to get it started but once you manage to get a gap it’s cake from there.