I recently ordered a 501B flashlight with a 940nm P60 dropin in it from a US seller. I sort of forgot about it and a flashlight from China showed up today. I thought it was a T6 that I snagged for real cheap. I put in a battery and nada. No photons for you! Hmmm, measure tail cap current. It’s pulling a valid current. Weird.
Ah ha! I think that I know what’s going on now. US seller is in China. 940 nm is in the infrared and that drop in puts out NO visible light. The proverbial Dark Emitting Diode. A quick check with the night vision equipment and all became apparent.
Now the problem is how can one tell if a light that emits no light is on? Click-on Click-off… it all looks the same. Something tells me this thing is going to kill a few 18650’s.
I also use this with any remote (tv, radio etc) that isnt working well, or not at all.
Just point your phone camera on the Led, and push any buttons on the remote. this will show up on your phone!
if it doesnt, then the remote is broken.
Convert it to a twisty tailcap, get rid of the switch. I did that for the old 501b mounted on my varmint gun. Even when it's OFF and backed out about 1/2 turn, the spring is strong enough to keep the contact broken, but there's enough slack in the crappy threads that just a little thumb pressure turns it on. Screw down tight and it's on. Unscrew more than 1 turn and it's locked out. In between it's momentary.
I replaced the all the switch parts with a similar thickness stack of metal, then reinstalled the switch retainer. Works nice.