I just got an S2+ with Nichia 219 from Banggood. It worked fine for a few minutes, but now it seems to be stuck on high mode. I’m not sure what I did, but I can’t access the configuration mode to change it no matter how many times/how fast I click the button. When I remove the battery and put it back in, the issue persists. Anyone know how to reset the firmware or something? Do I just have a broken light?
Reflector is shortening the diode.
Nah, Crisco does that.
Somewhere the black lead between driver and ledboard makes contact with the body.
Maybe a solderblob on the leadboard that is touching the reflector.
Or the isolation of the black lead is damaged where that lead passes the shelf.
Hmm, another reason to embrace TIR lenses… 
Have you checked to make sure the retainer rings on the driver and switch are tight? In case you didn’t know, the tail switch retainer ring tightens counter-clockwise.
I’ve got one with biscotti and sst20. It seems to be stuck at about 30 to 50. It was in the program mode with 100,30 and 1. No recent programming or drops and I don’t believe I had memory engaged. It had been flickering on occasion when the front end of the barrel wasn’t tight. I’ll fully disassemble it sometime soon to see if there’s any obvious problems anywhere.
Check all the retaining rings, especially on the driver (but also the switch; had [think it was] a TK05 that went mental because that loosened).
Unscrew, clean threads on both ring and hole, clean the contact on the driver/switch, rescrew.
Naw, couldn’t’ve been a TK05 (no tailswitch, duh), maybe a Tool AA.
Eh, whatever.
Guys, it’s a $10 light. It’s a roulette wheel at best as to how well it will work.
Having said that I have over 20 and I have almost no problems with them.
Absolutely positively worth $10.
This is and will always be my number one go to light.
I did fully disassemble it back then and found no obvious problems. I think it’s probably somewhere between 50 and 70%. Possibly the flickering caused some component a problem??
The last time I had a flickering issue with 1 of my flashlights, it was due to the contact between the spring and battery. I noticed (by chance) that if I held the flashlight a certain way, it would flicker. So I re-soldered the spring bypass to give more contact with the battery and the flickering thankfully went away.
I doubt that the flickering would cause an issue, but instead is due to an issue. And usually it’s due to a poor connection.
This is a resurrection of a year old thread .
The poster never made it clear if stuck meant you couldn't shut the light off or if it was stuck in a 100% single mode yet turned on and off .