Dead TK 75-HELP PLEASE!

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scotlarock
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Dead TK 75-HELP PLEASE!

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?

Streamer
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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?

scotlarock
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Yes they are quality batteries, 4 Keeppower and 4 Soshine. The protection circuit is tripping on both sets.

RaceR86
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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.

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aoeu
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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.

RaceR86
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aoeu wrote:
Is it stock?

scotlarock wrote:
So I threw my resister modded TK75 in my boat bag and headed out to the lake.

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ryansoh3
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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.

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comfychair
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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-.

scotlarock
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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!

ryansoh3
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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:

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comfychair
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ryansoh3 wrote:
Here's the crisp tantalum cap:

Those things sound like a .22 when they go off!

ryansoh3
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comfychair wrote:

ryansoh3 wrote:
Here’s the crisp tantalum cap:

Those things sound like a .22 when they go off!

Never heard either of them go off. Party

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scotlarock
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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.

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I’d be a sad cookie if my tk75 crapped out. I hope you’re able to fix it.

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scotlarock
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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.

comfychair
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You mean you measured from the B+ spring/pad to ground, and it did not show a short?

scotlarock
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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.

shimey
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scotlarock wrote:
Don’t think lockout is quite as easy on the TK75 as it is on the SRK.

Yep. When I fly, I take my battery carrier out and put it in backwards.

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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?

scotlarock
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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?

Ervin Anastasi
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I also believe probably there is some short, and that explain why safety is triggered in batteries. one of the things I will not do in this point is to put unprotected batteries.
u have to find where the short is. Am not familiar how tk75 is build internally but first thing i have to check is battery compartment, if he can be pulled out do the short again happen between + and – ?
if yes problem is there, if no than continue to check the path the + goes till the driver and to the led. somewhere in this path must be a short circuit which tigers safety mechanism on batteries.
from what you say i think to things can happen when you put on bag. one is like you say the flash turn on but it heated up very much being modified and lacking fresh air to cold so led can go dead but i thing is very improbable that ALL three leds go dead in the same time, so probability driver have gone dead heating to much and probably is shorting something. or some wire unsolder-ed from heat and also make short somewhere.
or if u drooped it hard somewhere something in battery section have moved and is shorting from plus to ground, but this is probably less likely to happen.

two batteries at 3.94v seems to have worked some sec at high before something go puff and short inside…

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comfychair
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If the short were on the output side (reflector touching MCPCB pads, or wire got hot and unsoldered itself, etc.), it wouldn't trip the protection until the light was switched on. It's not doing that, it trips as soon as the carrier is inserted & tail screwed on. It has to be something on the input side of the driver and not the output.

I've never been into one of these lights, anybody have good clear pictures of the driver?

scotlarock
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Comfy, I don’t own a good camera, and the pictures I took with my phone are not good enough to post. Anyone else have pics?

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Tom E wrote:

I forget, is the TK75 4 cells in series, and 3 LED's in series?

Cells are 2s2p. 3 leds in series.


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scotlarock
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Thanks for the great pictures, Racer. Update- I desoldered the battery contact board and checked for a short there, and everything is fine on it. So, the short is certainly in the driver itself.

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Check for shorts in the caps, the yellow blocks on the second photo and one on the first photo.

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scotlarock
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Thanks Ryan, how would I do that? Isn’t there always continuity across a capacitor?

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scotlarock wrote:
Thanks Ryan, how would I do that? Isn’t there always continuity across a capacitor?

Yup, you’d check for continuity with your DMM.

Capacitors will be shorted at the very instant you put your leads across it, but the resistance will rise to infinity as it charges and doesn’t pass electrons through.

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shimey
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scotlarock wrote:
@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.

Yes! Tailcap IS anodized, but I (forgot to mention) I cut a thin plastic disc that press fits in the tailcap for that very reason.

scotlarock
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Ok Ryan, The cap, in the second picture, to the left of the “big square thing” is showing continuity, all of the time. The other caps are acting like you predicted they would.

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scotlarock wrote:
Ok Ryan, The cap, in the second picture, to the left of the “big square thing” is showing continuity, all of the time. The other caps are acting like you predicted they would.

Great, we have a lead. The cap is directly across the battery inputs, and the shorted cap may be tripping the battery protection or something else along the two paths might be the culprit. If you can desolder the cap on the left, that will verify that it’s the issue.

Edit: Upon closer inspection, does it show any signs of overheating or damage?

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