My XM-L C8 from Lightmalls has a weird issue — when everything is fully tighten and switched on it does flicker and change mode by itself, quite unstable. But if I loosen the tailcap or body by a very little it works like normal. I disassemble it and checked all the contact area are fines, but it still doesn’t work well when tighten. By the way, I use Flames battery with my C8, does it has anything to do with the cell length something?
sounds like when you tighten the tailcap, it puts pressure on the driver in the pill creating the short. Check the driver and make sure it is soldered properly and making good negative contact.Make sure that the reflector is not shorting the output to the LED too.
Unscrew the tailcap, take out the battery and then shake the flashlight. Does the head area rattle? If so, open up the head and turn the pill CCW about a quarter. Repeat until rattle goes away.
Perhaps the driver spring is making contact with the inner body tube when tightened and creating a short.
I have tried re-soldering the driver positive spring contact again, checking the tailcap, cleaning the threads… and the flickering problem become even worse! I can’t think of any other possibilities, feel like just want to toss it away J)
Is it possible that the driver is having something wrong?
Did you dismantle the whole tailcap assembly or just checked it?
Pretty sure it’s the tailcap. I’ve had the same problem. Opened, cleaned and retightened the tailcap - that fully solved it.
Yeah, sounds like a tailcap/switch issue to me. Completely disassemble the tailcap, then re-assemble it and make sure everything is tightened up properly.
Ya I did fully disassemble it, check all the contact area and then screw everything back in. Done this few times already and seems like the problem only got worse. Should I do a bit of soldering inside of the tailcap to make sure everything is contacted and tight?
Have you done the negative pole to inner body tube tail cap check? Use a screw driver and remove the tailcap, touch the negative pole of the battery to the body tube where there is no anodising and it will turn on, or you could use a DMM. Apply a lot of downward pressure on the battery and check to see if you have the same issue, this way you can eliminate or determine if it’s a tailcap issue.
Good one, and I have just tried your suggestion. I do not have a DMM with me now while I just use a tweezer to close the circuit. It seems that the light works well even I applied strong pushing force on the battery, so I presume that what the above members mentioned are right, that it is the tailcap problem.
But when I disassemble the tailcap it seems that nothing is wrong and nothing is too complicated, BUT problem still exist 
By the way, I’m using Trustfire Flames battery and the battery is too long for the light body, that the tailcap cannot be fully tightened. If I force to twist and tighten the tailcap further, the light will shut off or flicker like crazy. Something is wrong inside when the battery is giving too much pressing force on the driver spring/tailcap.
Tomorrow I might try another approach: remove the driver spring (positive side spring).
sorry to ask but, did you clean up the tailcap bits when you removed them? Is it possible that the tail switch has broken contact with the board it’s soldered to? Did you spray WD40 (or better yet, Deoxit) in the switch?
These cheap components in budget lights - they’re made to just work as is - meaning they’re not really built to withstand any additional stress or variables.
Not worth it to diagnose too much into it IMO. Obviously something gives out under that compression. Easiest we just take out that compression factor.
I think you’re right in taking out one spring off - that will alleviate a lot of stress.
Could be the rubber booty is tight against the button, causing flicker and intermittent mode changing... If you feel no gap from pressing the boot to making contact with the button, and it's really sensitive to the touch, maybe that's it. You can remove the booty and trim the middle stem down just a little bit... I've done this before.
I bought Aurabuy C8 during the promotion period and I swap its tailcap with my Lightmall C8, and problem solved! Aurabuy C8 seems to have a good tailcap.