Many thanks!
Sorry for the dumb. I haven’t used my light (D4S v1) in quite a while. When I went to use it yesterday, it wouldn’t turn off. It’s stuck on. The only way to get it to turn off is to unscrew the tail cap. Pressing and holding the button or clicking it is doing nothing. Nothing changes (brightness stays the same). Is there some way to reset this light? I don’t know what I did to get it stuck on.
On this thread we’ve talked mainly about the sophisticated inner workings of the D4S (thank you TK!), but now I’d like to mention something about the ergonomics of this beautifully designed light, specifically the button, of which there are at least three important advantages.
1) The “hump” which provides instant tactile identification of the button’s location, something that is lacking and often a problem in many small lights with side buttons.
2) The recessed button which significantly guards against accidental activation. (I belt-carry the light in a small perfectly fitting pouch, much smaller and more convenient than the Bianchi 7307)
3) The anti-roll function of the “hump”, very important if you put the light, body-down, on any surface that is even slightly slanted.
These seemingly minor features add greatly to the comfort and convenience of using the D4S. Actually, point one is crucial in a situation where instant activation is required.
What pouch are you using and where did you get it? I’ve been looking for a better way to carry mine and would love any info you can give me.
I agree with you about the ergonomics of the D4S. I wish its features were available in a smaller form factor, because it is a lot to carry, but the upside is the way it fits the hand. The grip, the button, and the user interface all come together in an amazing way with this light.
What about the D4 / D4v2?
I used the holster/pouch that came with this light, the Thrunite TC20, which was my favorite before the D4S came out. Its output was similar and it was and is an excellent light, but relatively primitive compared to the D4S. I think that the pouch still comes with the TC20, but $90.00 is an awful lot to spend on a pouch, and I saw no option to buy the pouch separately, so I briefly looked around Google and saw a few things but didn’t follow them up. Of course there’s always that Bianchi 7307 which, while not ideal is perfectly acceptable.
https://www.amazon.com/gp/product/B0013AWP6I/ref=ppx_yo_dt_b_asin_title_o06_s00?ie=UTF8&psc=1
Good luck 
It sounds like there may be something physically wrong, but it’s hard to say what exactly. If you loosen the tailcap to cut power, then tighten it again, what happens?
Wow that’s a pretty impressive light.
FYI I’m using the Maxpedition single sheath pouch for my D4S. It’s a fairly snug fit with the elastic band around the middle, but the elastic can be stretched or even cut off if desired.
When I loosen the tail cap and cut power, the light goes off. When I tighten it back up, the light comes on and stays on until I loosen the tail cap again (because I can’t get it to turn off any other way).
Okay, sounds like there’s definitely a short or a dead chip in the head of the light, then. It could be the 7135 chip, the FET chip, or some sort of other contact between LED- and ground. In any of those cases though, hardware repairs or replacements would be needed to get it working again.
If you have a way to measure the brightness, it may be possible to narrow down the possibilities… like, if it’s running at a steady ~130 lumens, it’s probably a dead 7135 chip. If it’s running at 1000+ lumens, it’s probably the FET or a driver bypass of some sort. But that probably doesn’t matter unless you’re planning to repair it yourself.
There were more changes with that upgrade. This thread should give you everything you need about that:
Thanks for the info!
I haven’t found a source for the pouch by itself, but I will keep it in mind.
I may have one of those around. I would have thought it was too small, but I’ll give it a try. Thanks!
NOTE: If you or anyone else gets this pouch: It was bit snug but I widened it to perfection by pushing in an object (small glass bottle) of significantly greater diameter than the D4S, and letting it sit overnight.
The Trustfire holsters sold on Amazon will work.
Here it is on Amazon and it will accommodate flashlights up to 6”. The D4S is only four and one eighth inches long. The way to avoid having 2 inches of empty holster is to glue a small length of Velcro below the existing Velcro, then fold down the cover to D4S length. This will allow you to have a well-fitting holster. The info states that it will accommodate flashlight diameters from 35mm to 50mm, but the closeups show the same weave over the entire case, as opposed to a visible stretch weave. Therefore I’m a little skeptical about how comfortably the D4S will fit.
That’s the one. It does work. There will be less than 1/2” of empty holster at the bottom, but of course if that bothers you, stuff in a small piece of bubble wrap or foam or whatever. Yes, you would probably want to glue on a small piece of velcro to close the flap more, or not. Won’t fall out.
That sounds like you have the holster. Does it comfortably fit the width of the D4S; can you easily place the light into the holster? Because the photos don’t show a visible stretch weave, unless the whole thing is an unusually woven stretch weave.
Yes I have it. It works. No stretch.
the one thing I do with a holster like this is cut off the ring on the back then reinforce the top of the belt loop with a couple of rivets (if you don’t have that setup your local shoemaker should be able to do it for you). The bottom of the loop is fine, the top is only one row of stitches so I don’t trust it.