thrunite tn31 help

hello to all, i have a tn 31 that stopped working i checked the 18650 batteries with multimeter each one has 3.7 volts.
and checked tail cap switch with ohms it showed to be good.i think the problem might be in the head of the tn31.
im new to this so any suggestions on what i should check or test next. also i looked at the LED bulb with a magnifying glass and didn’t see any cracks or bubbles.

thanks,randy w.

p/s any help would be greatly appreciated.

I believe the Thrunite store sell just the head too :slight_smile:

Check if the cables to the led got unsoldered.

Check if the battery carrier is giving 12.6v

Most likely doesn’t apply to you, but did you check proper battery insertion?

Can you make a 3s pack to connect it directly to the head to see if it works?

Did you open it up for any reason?

Are the sense resistors loose? Is the plastic ring around the spring in the head missing?

I had a TN32 stop working as well. There's pictures of the problem here and may or may not be your problem.

I did not get a response from Thunite. l hope you have better luck.

Man, the TN31 is a pretty complex light with a lot of parts and contact points. I guess I would start with AlexGT's suggestion. If that doesn't work, I would pull the emitter and test it out of the light. The head has thread lock. I put mine in a plastic bag in boiling water for several minutes and then used leather gloves to unscrew it. It was still quite hard to open, but my strap wretches would not grab.

I'm pretty certain my emitter would have had a very short life if I had not modded my TN31. The emitter base was sitting on a small nipple. The nipple kept the emitter base from even contacting the thermal paste.

Charge the batteries to 4.2 volts.

Thanks for all the infomation,i did reach customer service at trunite store via e-mail,they told me i could return the tn31 for repair but i didn’t want to ship it to china.so now i will get inside the head of the tn31 and check the suggestions made by alexgt.

thanks again for all the help,
randy w.

Before you open the head, I would proceed with building a 3s pack and connecting it directly to the back of the head (IIRC the spring is +) to a 12v power supply to see if it works, if it does then I could try and unscrew the stainless steel crown to get access to the led and use a 3v battery to connect to the mpcb to see if the led works in direct drive, if it works then I proceed to open the back plate of the head to check the sense resistors and check if the led cables are lose or have a bad solder, also check if the magnetic control thingies (forgot name) are not bent. And check if the plastic ring around the spring is not missing.
Good luck

Ps if you do open the head be careful not to loose the very small spring and metal detent ball located inside the control ring

thanks for this information,alexgt
can i use the battery pack that came with light and jump wires to tn31 led head for 12 volt test or what would be the best way to get the 12v source.

Yes insert the batteries in the battery carrier, check with DMM if you get 12.6v (Fully charged batteries) if you do carefully, run a wire to the head , center metal screw should be + and the plate with the screws should be - run the wire to the head spring is + and plate is - make sure you select a power setting, then test the light

If it works, the problem will be in the switch, if it doesn’t the problem might be the led or driver

BTW have you checked that the central + screw is free of dirt and oil and screwed in tight on both sides of the battery carrier? I had problems with that part on my first TN-31 the problem was that the central screw was loose.

check here for instructions

alexgt, ok i have the Panasonic NCR18650B Protected 3400mAh 3.7V 18650 Lithium Batteries on charge right now,
i will let you know what i find out.
thanks so much for helping me.
randy w.

i got another tn31 since the price went down,so i used the battery carrier from old tn31 in the new tn31 and it works great.so now should i take the 3 screws out of the control dial ? to see what i find.

thanks randy w.

Good to know that the battery carrier is not the problem, did you try switching the heads to check if it is not a switch problem? if it is not, then I would take a look a the driver in the faulty TN-31

i just checked the old carrier holder and tail switch with new head and it worked.so the tail cap switch is good.

thanks,randy w.

p/s i’ll preseed to take the head apart. i will let you know what i find.

I would first try and connect a 3v battery directly to the LED to see if the led works, if it does then it would definitely be a problem with the driver. make sure you got the polarity correct (+ led with + battery // - Led with -battery)

i removed the 3 screws that holds the circuit board in, and noticed that the large resistor was loose.
not attached to the circuit board. any suggestions on how to correct this problem would be greatly
appreciated.

thanks,randy w.

Have you a picture of the loose resistor? It sounds similar to a problem I had.

here’s the picture of the thrunite tn31 circuit board with loose resistor.

Just hold it down and hit that tab with a soldering iron. Really easy to fix that.

Hi

This is not a resistor, is a coil, It can be welded again, then you can put some glue to hold up better :slight_smile: