Fenix TK61 teardown and mod thread

Dale, lately I've been moving towards the hot dedome method. This is purely anecdotal, but I seem to be getting slightly less green shift with this method. More risk, but perhaps more reward. I have killed a few emitters doing this, but Lisa couldn't put up with the smell anymore! Our apartment makes things difficult sometimes, and even though I try and do almost everything outside, some smell always makes it in.

I'll post full details tomorrow if all works out, but I've got mine cranked up to 5.8A to the emitter now. There is no way the stock driver MOSFET(s) could handle this kind of current, I have a few burned fingers to prove it! (low tech thermometer! ) If it survives a few 10 minute runs on high, I'll post details here. I also have a stock light to compare it against and get some readings from (lumens, lux.) I put the stock emitter back on the stock MCPCB, so the two lights will be equal in that regard.

Both the hot de-dome and the 5.8A. Will be watching closely…

Hot de-dome at time of re-flow? I heard that a med firm press on the dome right after re-flowing the emitter makes it pop right off. Haven’t tried it.

Some of my best dedomes have been accidental!

Here's how I do it (very similar to Vinh's method on Youtube.)

1. Heat emitter until solder flows.

2. With a sharp knife, quickly cut the corners and end of the base of the dome opposite the bond wires.

3. Reheat until solder flows again.

4. As soon as solder solidifies, take your knife, slide it under the dome, and quickly pop it up and away from you (towards the bond wires.) If you do this while the dome is still hot enough and with enough precision, you will have a nice dedome. If you don't, you will have potentially lost phosphor, broken bond wires, or a dome left partially in tact. I have killed a few emitters doing this, but have been mostly successful. XP-G2s are much more difficult to do this way since they are so small!

There is a bit more risk involved with this method than with the gasoline method, but some may feel the tradeoffs are worth it.

Please post back, eager to know!


Fingers crossed you get it to work.

Since the TK61 have two buttons. Could use one as a mechanical power button and the other for electronic switch. :)



@RMM looking forward to hear more about your progress. Will you stop experimenting if you get it to run reliable for 10-15m at 5,8A?

Regarding Dedoming. Could we keep that to one of the many threads that already started?

One of the relevant threads, and a video too.

A Perfect Dedome?

I noticed on my lights that the MOSFETS around the resistors looked a bit melted. Id guess its because I held the solder iron too close when playing with the resistors. Or they have seen too much heat when I did some indoor runtime test. Its recommended to use thermal pads. I don't use that on my light simply because I want to see how the driver handles it without. J)

WOW i can’t imagine anyone run this light 15 mins perma on turbo, isn’t it too much for this modded lights?

I never run more then 1/2 mins max on turbo, even on stock…always circle around the mods.

lol.. 1-2 minutes? On a light of this size thats only running a few amps.

Unless a light can be used until its uncomfortable hot its no good IMO.

My hottest light (so far) is my hotrodded tintmixed/widespecturm 30+ amp 9-XM-L fandyfire. The front of the head can reach about 140C/280F in around 15 minutes. I wont dare to think how hot the 12 XM-L light pictured in OP could become once that is pushed way harder. 0:)

My first runtime test after I resistor modded the TK61 was around 15-20 minutes on Turbo. I just did another one at 30 minutes. Indoors. No breeze. Tailstanding. Quite hot indoor temperature. Gets uncomfortable to hold after around 15-20 minutes. Too hot for me to hold after 30 minutes. Outdoor I would expect it to run from full to empty batteries on Turbo without issues.

Again, I cant speak about long term reliability, but real outdoor use will never see anywhere near the temps I get indoors.

But i don’t understand, if you are not professional or some search and rescue, why do you need super mega 1600lm, and like 500.000 cd constantly for 15 mins? for example last night my TK75 was modded to ~ 4400 lumen, or 4.68A (based on some other user measurements with same resistor R015)

The light has become insanely bright, like stupid bright, now compared to before OMG effect.

The light heats up like ~ 40% faster or even more. I was going from turbo > high like on every 30 seconds, i just don’t need constant turbo if its not real need, for fun few mins on max and cycle is pretty good for me…while still having low temps and better relaibility - less pressure on the light.

BTW this lights T (K75/61) have no over temperature protection afaik, so i would strongly advise against testing modded lights in hot rooms without fan……you have no need for that, just a friendly advise.

Some of us want to play with em, have no real need to use em. Others want to be able to put a light to work, and do exactly that. Mostly I play with the lights I modify, I take them walking to take the trash down to the road once a week, a 300 yd walk down and then playing with Turbo and such on the walk back, stopping to compare and test along the way. But sometimes I have need of a light to use, and then it’s from 10-15 minutes to maybe hours. So I like to keep in mind that any light I build may actually be put to work. I expect it to handle that, or what’s the point? I know I’ve modified some lights to the point that the higher levels will burn through the cells too quick to be useful, but am trying to use more levels now so there will always be a position that can be selected for an optimized power/runtime equation.

And such is the nature of the beast. Letting the desire for MORE overpower the actual needs is all to easy. But, a change of scenery can often show that what we’re happy with at home may not be viable elsewhere. A cave, a mountainside where the valley is distant, wide open spaces can devour even the biggest baddest light out there. Large bodies of water do the same.

For me, it’s just finding that I have the ability to push a light to it’s extreme. I’m having fun with it, and right now that’s what it’s all about. :slight_smile:

Yesterday I took my wife shopping form some new black slacks to wear on photography shoots. Carried my MT-G2 Sinner Ti as is now my custom. In a nice store like Dillards, having the MTG2 was very handy, making it easy to see the navy blue vs black. :wink: Without the light, I was getting it wrong under the store lighting. Put em to work…

I understand the need to have a massive amount of light, but now with the mod, my high is like 1600 lumens, so you want to say that that’s not enough for a walk? :smiley:

I know i know wrong forum to say hat buy still :smiley:

Generally i use 400 (now 500 lumens i guess) mod from my regular yard checkups, sometimes i blast full power of 3000 lumens which illumuinate my whole yard, and i can imagine now with ~ 4.400 lolz. Anyway i hope you guys don’t get me wrong, i love massive output lights, but just i’m used to cycling trough modes, and no that’s not to preserve the lights, its just an habit, don’t know why i do that :slight_smile:

We have some pretty awesome storms roll through, and with the fast growing Hackberry trees on fencelines (courtesy of the birds) we routinely have a large tree down from high winds, and usually across a road out in the country. We don’t wait for the County to come clear the road, but voluntarily grab up the chain saw and clear the way. My 5000 lumen M6 will be great for lighting up such a scene, but will it last for the hour or two it’ll take to cut a 28” thick tree into small enough pieces to clear the road? Maybe still in the rain?

Repair a fence after a drunk drives through it and hopefully before cows get out? Black cows? In the night? With wide open spaces easily a mile in length? 1600 lumens isn’t enough. Unless it’s focused like a laser. :wink: [not difficult to repair the fence with lesser light, but finding the cow critturs is another story altogether…]

Keep in mind, your situation is quite rare, i’m talking generally here, you have the real need, but not all does :slight_smile:

That’s why i said if you don’t have the real need, serious rl scenarios, its not a must. Cheers :slight_smile:

If your TK75 is running 4,68A at each emitter. Assuming that is what you mean. You are looking at 14 amps divided on 3 emitters. That is a whole different heat level than the 3A or more from a modded TK61.

Why would I not want to run a 1600lm 500kcd to run for 15 minutes? Or at least know its up to the task. Why would you want to dim down all that glorious throw if you have the runtime for it? :D

If im up on the mountains when its dark its useful to have good range. And I can use all the range I can get. Same if you are in a boat. You can never have enough light or range from a handheld flashlight. I even enjoy being able to light up mountainsides when Im at trails beside them.

Even just for fun I still enjoy pushing limits and lighting up things in the distance. Why have 1-2 minutes of fun when you can keep going longer...

Doing some extreme testing indoors is useful to know if it will handle the heat. I never post anything about a resistor mod unless it seems to be somewhat reliable in a bit of extreme testing. When that is said. I cant guarantee anything about reliability really. But I can do tests that can help others to get a better picture of what the light is capable of or how it acts.

Like Dale said, I actually expect my flashlights to handle some work if its put to the task.

What is the point of buying a Ferrari, get in tuned, and then barely use it above 4000 rpm and never run it faster than 50 miles an hour or slower? I like to be able to use certain things. Id like to know something is up for the task. Any task its supposed to handle, and if its not. I will improve it. That is what modding is all about to me. Improving lights. If I have made an unreliable light, then its not a good mod. Id rather find the limits of a light indoors, than outdoors when its actually needed...

Pushing a light well beyond 100 Celcious might be a bit over the top. I tried to make an omelett on my 9 XM-L light btw. 0:) Maybe I made a multi purpose camping light. You know, cooking stove and flashlight all in one. :D As long as emitters are mostly below 150C and as long as the batteries are below 60C, and as long as driver circuits can be replaced, I don't have issues testing limits. I even enjoy it.

Need at least 3000 for a walk.. 1600 lumen is so 2013.. lol

dazed1, not rare at all for the 20 million people living in Texas. Just sayin…

Hahahah you made me laugh for sure with the 2013 part :smiley:

Anyway, i guess i’m like this because i use 95% of the time my lights for urban areas i live in the capitol city :frowning:

BTW i never said i don’t use my lights on turbo, i’m just more for different turbo usage, turbo few mins > high > low, then after 10 seconds again turbo and so on…

So yea, its similar runtime, just not constant. BTW about the amps, not really sure how that works, but i guess its ~ 4.6/4.7A per led? i’m confused by all of this driver (regulation)>cells>parallel>series things, so i’m not sure but i think you are right, its 4.7A per led, resulting in 14A….

Also one more thing, i heard that when volts drop, the amps rise, but is this drain from cell only? i’m guessing the amps to the leds never increase more then 4.7A right? sorry still just a noob :smiley:

If it can't hold up to 10 minutes turbo, it's no good. This is a $200 (modded) super thrower and it should be able to run until it gets too hot to hold or until the cells die.

@RaceR86, did you do all of this testing with stock transistor? (runtimes indoors)

No reasons to test before. Its built to handle 4 hours and 20 minutes on Turbo when stock. Or about twice that time if you have the battery extension kit of whatever its called. Basically its built to handle full output all the time. Like pretty much all lights...

I did two runtime tests after resistor mod.

I hope to give you some exact numbers regarding the modified TK75 in the distant future. ;)

Yupp.. Thats pretty much what I tried to say when I wrote that wall of text above. :D

On a side note. I bought my light from WB. TK61 is now back it stock from BG and slightly lower price than earlier. A tad cheaper than WB after coupon code are used in both stores it seems.

So let me get this straight.

You get the light to 4.8A from 3A at stock, with only resistor swap right, nothing else added?

And you did 2x runtimes ~ 30 mins each on turbo (one of them indoors you said?) without any issues at all? that’s totally impressive, knowing that it was suggested to me to not go over 4.2A for safety reasons (and even that can be dangerous)

Anyway, just to be on safe side i will wait for RMM and maybe your findings about new transistor (s) you guys have any idea of what can be used for reference? thanks.