So I threw my resister modded TK75 in my boat bag and headed out to the lake. While pulling the light from the bag later, I noticed it was quite warm. I believe it got turned on in my bag. Back home I checked the batteries 2 were at 3.94v and the other 2 had their protection circuit tripped. I put in a fresh set of cells and the protection tripped on one of the cells again. Removed the driver and inspected for obvious things and found none. I have heard that Fenix will not sell individual parts, so replacing the whole driver is out of the question. Any ideas?
Are they Quality 18650 batteries? Do you have others to try than those same sets of protected you've been using to rule out faulty batteries?
Yes they are quality batteries, 4 Keeppower and 4 Soshine. The protection circuit is tripping on both sets.
What type of resistor mod did you do?
I might have a spare TK-75 driver if you want one. PM me later this week, Ill know then.
Is it stock? I would think a torch for that price would have some sort of idiot-proofness built into it to prevent such straight forward accidents from killing it.
I wonder if it’s a dead short in the driver, not sure what turning it on for a long time did to it.
Do you have a multimeter and a set of unprotected cells or a bench power supply? You can try to measure the current it’s trying to pull.
Does the protection trip if you put fresh cells in but don't switch the light on?
Check for dead shorts at both the driver B+ and ground, and across the driver outputs at LED+ and LED-.
Thanks for the responses;
@ Racer- Removed stock sense resistors and replaced with lower value. I did this several months ago and use this light frequently with no problems. You can feel a significant amount of heat in the driver area, when running on turbo. This light was in a full bag probably wrapped in clothes, when this happened. PM coming!
Ryan-I do have plenty of unprotected cells, but am somewhat reluctant to try them in the light at this point. Comfy-The protection trips on one cell as soon as I load the carrier in the light and screw the tail cap on, before power switch is pushed. When I get a minute this evening I will perform some of the tests you mentioned.
Everyone’s continued thought on this is much appreciated!
Yeah, I also don’t think it’s a good idea to try unprotected cells if the protected cells are tripping as soon as you insert the cells.
I’d recommend opening up the driver and seeing if there are any shorts or burnt components, mainly capacitors.
I had this happen with a Jetbeam DDR30. One of the capacitors had blown up and was shorting out the inputs.
Here’s the crisp tantalum cap:
Those things sound like a .22 when they go off!
Never heard either of them go off. :party:
Yes, I did remove the driver and check for obvious things (dead shorts, burnt components, burnt traces, etc) and found none. I don’t have the knowledge necessary to check each individual component for proper function.
I’d be a sad cookie if my tk75 crapped out. I hope you’re able to fix it.
Lol, I am a sad cookie! I use this light a lot. Some of you may have seen the post I had about a year ago when I did the same thing with an SRK and ruined 3 of the 4 “protected” batteries. You think I would have learned. These electronic switch lights need to be locked out before being packed! Don’t think lockout is quite as easy on the TK75 as it is on the SRK.
You mean you measured from the B+ spring/pad to ground, and it did not show a short?
When I check continuity between B+ and B- it shows a short. I also checked between B+ and the outside ground ring on the driver, still mounted, and that also shows continuity.
Yep. When I fly, I take my battery carrier out and put it in backwards.
You sure all 3 LED's are working ok? I've been fooled before, thinking driver problems. It would be good to know 100% before driver swapping (I sure know that...).
I forget, is the TK75 4 cells in series, and 3 LED's in series?
shimey-both the positive, and negative, terminals are raised, and on the same end of the battery carrier. I don't see how turning around the carrier and screwing on a solid aluminum tailcap wouldn't short out the carrier. Tom, I don’t know if the LED’s are ok. I haven’t tried powering them from an external source yet. I believe the carrier is 2S-2P as it shows 8.37v with un-tripped cells, then after inserting the carrier and removing it shows 4.18v. Think Comfy is on to something here with the dead short between B+ and ground. Now how to fix this?