Thrunite Neutron 2C V2 Teardown

       I have a bunch of flashlights and this was my favorite EDC. Mainly because of its small size and decent output, nice choice of brightness modes (no blinky modes!) plus the neutral white tint. The only thing I did not like about it was that it often accidentally turned on in the holster and sometimes got hot.

       This will not be a complete review (read one here ) but just a few pics of how mine failed.

       As with decent quality lights, I assumed it is water resistant, or even submersible at shallow depths as it had decent o-rings for seals. I guess I was mistaken. I got it last Dec 2015, submerged it a few times in seawater and it was just fine. Took it canyoneering on January and it had moisture on the lens, dried it up and it worked fine after that besides some pitting on the reflector. And then a light dip in the pool just this month and it then stopped working without any sign and I found some water when I opened it up - I guess that finally did it.

This was my light. It is slightly scuffed being my EDC.

Nice engraved letterings.

The front window is antireflective coated.

The reflector is slightly dirty as water had previously entered but it still worked.

The light could take 18650s or I sometimes use an 18350 cell to make it small if I don't need the extra run time.

The XML2 LED is nicely mounted on a metal core PCB.

An allen setscrew is used as a pin to prevent it rotating when the front is tightend on the LED assembly.

The metal core PCB is copper based which is very nice.

One side of the sub board. It is very densely populated. The greyish square object in white gunk is the main power inductor and is decently rated.

Top side uses a uC for the modes and on/off control. Some other support components for the LED driver are also seen.

The back side has a metal disc as a reinforcing contact so that it can make a good connection even with flat top cells.

The front head disassembled.

There is also an o-ring sealing the front lens so this is supposed to be reasonably water tight.

This is the suspected point of entry.

There is a slight hint of rust on the pin.

When the button is removed, everything is now clear.

If the flashlight got submerged or had been resonably wet, water could get in and stay under the button and keep that area wet.

The spring that keeps the sealing o-ring compressed has rusted and it lost its strength.

This resulted to a poor seal and it soon failed.

I hope Thrunite replaces this with a stainless steel spring for better reliability.

       After having it for only a few months, I really loved it except for the accidental turning on and the poor water resistance.

       This one is beyond repair as there have been a bit of corrosion and I knocked out a few parts trying to get the glued PCB out. If the PCB had been conformally coated, it should still have worked except for some pitting on the reflector surface. It was a shame as this was a well designed light but could have been perfect if not for the things I mentioned above.


20 Apr 2016:

       A few email exchanges later with Thrunite customer service, they said they are willing to replace it with another light of similar value even if I have opened mine trying to fix it. Although it would take a while since I have to have a relative bring it over to the US and have it shipped to their US adress and Thrunite only ships within the US. We shall see and it seems they have good customer service too.


21 Aug 2016:

Finally have my hands on the replacement light, it took a while as I had to have a relative in the US to ship it to them, get it back, then wait for someone to return and take it to the other side of the globe. Unfortunately, they did not have the Neutron in stock so they sent me an Archer 2A V3.

I wanted a neutral white light just like the Neutron but they also did not have that version in stock so I just had them send me the cool white version.

This won't be an in depth review. There are lots online since this light has been out quite a while.

First impression is that it is really slim. Nice for a EDC.

Here it is beside my only other 2x AA light, a Fenix E21.

Second was that it was a very wide flooder. A very small lens and a large XP-L emitter makes it floody but perfect to me. Good for using during emergencies or when I'm working on something.

Reflector and LED is clean, no spots of dirt or dust and glass lens is also coated which is very nice.

Button is kind of wiggly, not unlike the solid feel of the Neutron's. It feels soft underneath which means there is a rubber pad of some sort for sealing but does have a really positive click feel to it. Does not feel like it has springs underneath that will rust.

When I was playing with it, I noticed the beam seemed warm-ish and not cool white. Here it is beside a cool white Fenix E21 with a cree XP-G LED on the left, Archer 2A V3 in the middle and Fenix TK35UE which uses a huge neutral white Cree MT-G2 LED.

When side by side, The E21 is pure white as to be expected, The TK35 is white with an orange-ish tint to it which is a real neutral white LED beam. The Archer has a yellowish with slight greenish tint to it. When used alone, it looks yellowish and the green tint is not noticeable.

All the lights were about 2m from the wall so you can clearly see how much floody the Archer is.

        As an EDC, I like this light. It appears to be as nicely designed as the Neutron so I expect the internal assembly and circuitry to be just as good. It is slim, lightweight and portable enough but still packs a punch in light output. It does get really hot quick on high which is not much of a downside as it will run the AA's down pretty fast. The firefly mode is what I'm after as it is very helpful when you need a very small amount of light in total darkness or when you just woke up in the middle of the night. Last thing you want is a blast of full output into the retinas. The pocket clip would have been nicer if it is placed more at the back, or atleast a spot to put it there so when you slide it into a pocket, the tail does not pop out as much. The button and tint comment is a little nitpicking but I could live with those, I think it is still a great light.


24 Aug 2016:

After a few days of using it, I noticed where the yellowness is coming from.

Much of the yellow is on the center spot of the beam. The flood or sidespill is pure white if you cover up the center beam.

With the light in firefly mode, it can clearly be seen that the yellowness is from near the middle of the reflector which reflects the light emitted by the LED nearly perpendicular to the front. This is very yellow as it is mostly the output from the phosphor and none of the blue LED chip output is coming out the sides.

If the reflector is made a little deeper and the LED sits a bit lower, the yellowness would be gone but there would be some loss of lumen output.

Not really sure if it has something to do with the XP-L package which fits an XM-L2 die in an XP-G package. Maybe the XP-L high intensity package would have worked better?


19 Jan 2017:

Short story: Been using this light for some time and it started having an intermittent fault after accidentally dropping it face first into concrete. You'd sometimes have to hit it on the tailcap and it will then work. It would sometimes need the percussive maintenance, and sometimes it would work just fine.

Today, I was working on my car and put this light on my lap. Forgot about it and when I got out of the driver seat, it fell to the concrete garage floor and it no longer worked. Perfect reason to finally take it apart.

A lot of scars from being an EDC. I always have it clipped on my front left pocket wherever I go and it comes pretty useful at times.

The nylon strap broke and replaced it with stainless wire and a stainless link. Much stronger but rubs the anodizing off.

It took a bit of work but heating the head with the hot air tool to hot enough that I could not touch it and then putting it into the vice and turning the head with pliers while hot finally broke the threadlocker bond. They used a bit of threadlocker on it.

The threads are nice square cut.

The PCB has a nice springy gold plated ring to ensure good contact to the flashlight body.

Very nice attention to detail there.

A bit more heating and twisting, the front end came off.

They used a different kind of threadlocker here. It was sticky and yellow colored.

A view of the Cree XP-L LED.

The LED heat spreader pad is screwed in to the body unlike cheap lights that rely on the reflector pushing on the LED and then squeezing the heatsink pad to the body.

More engineeringg plus points.

Copper LED heat spreader.

More plus points!

The LED leads desoldered (Which are nice silicone wires!) and some wiggling.

Finally the driver PCB comes out.

It is quite complex with three boards in a 3 dimensional arrangement.

Silicone added as vibration/mechanical support of the parts.

A little too much force was used and the contact ring got a bit mangled but it can be reused no problem.

I was not able to take a pic of the underside of the button but it was a metal pin directly actuating the tact switch. A rubber surround could be seen and it looks like the seal is a little better than the Neutron. I have not tested it in water though, the whole time I had it.

A PIC 12F683 is used as the brains of this light.

A bit of desoldering and the complex arrangement is taken apart.

All the silicone glue was carefully removed and cleaned.

PCB silkscreen is pink!

This is the contact board.

It contains the microprocessor and a few support components.

Contact side.

Battery + has a metal disc as a nice contact point. This makes much better contact than bare PCB pads for long term use.

This board I would think is the control section of the boost converter.

The back side has the main power components. Inductor, switching mosfet, output diode, bulk caps and control circuitry.

The button on the third, smallest board.

Back side has a few more parts. These do not directly connect to the switch in any way. They are used along with the switchmode control circuitry.

I found this joint a little lacking so I added a bit more solder to it.

Not seeing anything wrong, broken traces or any fractured part, I decided to resolder ALL the components on all three boards except for the switch.

Ended up stumbling upon this resistor when I was retouching its joint, it moved. It is connected to the uC, not really sure of the exact purpose.

I replaced it with another from the scrap PCB bin and cleaned everything with IPA, reassembled and crossed my fingers.

And it worked! Happy that I have my EDC back.

What I think happened is that when it hit the first time, the force of the two cells moving forward and the PCB taking all that shock broke the end termination of the resistor. The last fall finally did the joint and it no longer made contact and stopped working.

Now that the threads are cleaned and no more threadlock, I can open this anytime to fix it if necessary. Yay!

        As with my previous Thrunite light, this one is also nicely engineered. Lots of details that most users will never get to see. They work well and are really nice, I just seem to have bad luck with their reliability or I abuse them too much. Still a nice light for most users though and I like the features very much. I was also able to measure current draw as I can now reach the front terminal easily. The numbers are for firefly, low, medium and high respectively. With 3.0V battery voltage: 5mA, 50mA, 190mA, 1.8A. With 2.4V battery voltage: 8mA, 55mA, 220mA, 2.7A.

Page created and copyright R.Quan ©15 Apr 2016.