Problem with my Surefire U2 - update, *solved*

First let me apologize if I'm posting this in the wrong forum, I do a lot of reading here but rarely post.

I have a Surefire U2 that I absolutely love. After I lost my first one on a camping trip I immediately found and bought the one I have now from someone here on CPF. Unfortunately the one I bought here wasn't as bright as my previous one so I started reading on here and decided to get it modified. I had the LED upgraded and I had it bored for an 18650.

So on to my problem. For the past few months I've had a problem with the light "strobbing", that's the best way I can describe it. When I activate the light with the momentary switch it's fine. But when I click the switch, 75% of the time it will "strobe". Slightly pressing on the switch will normally get the light to fully activate. I also notice if I start the light with the lowest setting it's fine but if I I turn it up it will start strobbing unless I tap on the switch and it clears up.

This is becoming annoying. I love this light and want to fix the problem. Is it the switch? Or a problem elsewhere with the light? I called Surefire today thinking that they would tell me it's my switch and they would mail me a new one. But they want me to mail the light to them so they can take a look at it.

Will I have a problem with Surefire over the modifications I've made to the U2? Is this something I might be able to fix? Just wondering what my options are. Thanks for any help and/or advice.

Re: Problem with my Surefire U2, need advice

The tailcap is probably the cause if the momentary part of the switch allows
normal operation but the latch part of the switch does not. I'm guessing there is some added
resistance within the switch that is causing a reduced current to the head of the torch.

Have you sprayed some contact cleaner/lube into the switch to clean it up?

Re: Problem with my Surefire U2, need advice

jimmy1970 said:

The tailcap is probably the cause if the momentary part of the switch allows
normal operation but the latch part of the switch does not. I'm guessing there is some added
resistance within the switch that is causing a reduced current to the head of the torch.

Click to expand...

And, the classic way to see if it is the tailcap is to take the tailcap off, use a paperclip to short the bottom of the battery to the bare metal on the tube. It the light works normally, the tailcap is the prime suspect.

SureFire certainly might not fix a modded light with an emitter swap. On the other hand, I have had them send me a new tailcap after they talked me through the paperclip test on the phone.

Was your second less bright U2 an early Luxeon model with a serial number starting with 'A' perhaps?

A worthy successor to the U2 is the UM2 discussed in this thread:

http://www.candlepowerforums.com/vb/showthread.php?410582-Surefire-UM2-Ultra

But, at least one of the owners reports a tailcap problem. :thinking:

Re: Problem with my Surefire U2, need advice

If you happen to have any of the traditional 'P' SF's (or comparables), the classic Z41 twisty tailcap is compatible with the U2, and is another method that could help isolate the issue.

BTW if you could give us some background on the mod (~6V or ~3V?), that might also be of benefit. The more modern LED's have lower Vf's, which /shouldn't/ be an issue for the driver (especially since you're running a single LiIon) - on the other hand, the U2 has a relatively-complicated driver and a component in it could be marginal and/or failing.

Re: Problem with my Surefire U2, need advice

The U2 is normally fitted with the Z59 tail cap. How many amps is your modded U2 pulling? The factory cap cannot reliably handle 4-5 amps... the small internal spring is too small for that current. Some later Z59s have had internal fitting problems.

My own early V59 has been bulletproof but I still installed a Z41 with a Mclicky and eliminated it as a potential problem when I installed an Oveready/TorchLab v5 triple on my first generation U2 body.

Good luck with your issue. [emoji41]

Re: Problem with my Surefire U2, need advice

Maybe also try running the light on a couple primaries at some point? While the U2 does typically run on a single rechargeable. It never was designed around that Vin. Might be of some use at further down the road if you continue to see the same issue your having.

Re: Problem with my Surefire U2, need advice

jimmy1970 said:

The tailcap is probably the cause if the momentary part of the switch allows
normal operation but the latch part of the switch does not. I'm guessing there is some added
resistance within the switch that is causing a reduced current to the head of the torch.

Have you sprayed some contact cleaner/lube into the switch to clean it up?

Click to expand...

I didn't think about the contact cleaner but I'll give that a try and see if it helps. Thanks for the suggestion.

Re: Problem with my Surefire U2, need advice

Vox Clamatis in Deserto said:

And, the classic way to see if it is the tailcap is to take the tailcap off, use a paperclip to short the bottom of the battery to the bare metal on the tube. It the light works normally, the tailcap is the prime suspect.

SureFire certainly might not fix a modded light with an emitter swap. On the other hand, I have had them send me a new tailcap after they talked me through the paperclip test on the phone.

Was your second less bright U2 an early Luxeon model with a serial number starting with 'A' perhaps?

A worthy successor to the U2 is the UM2 discussed in this thread:

http://www.candlepowerforums.com/vb/showthread.php?410582-Surefire-UM2-Ultra

But, at least one of the owners reports a tailcap problem. :thinking:

Click to expand...

I've tried paperclip test as part of the troubleshooting with Surefire in the past with a total failure of the tailcap on an E1B I had but I do not think that troubleshooting method would work in this case (especially since it works under momentary). Either way, I'm sure Surefire would have had me try that if that was the problem. No idea what my previous U2 was but yes my current one is an A prefix U2. I had Nitroz upgrade it last year to I believe an XP-G2 emitter. As far as the UM2, my plan is to order one in the next couple of weeks before they are all gone.

Kestrel said:

If you happen to have any of the traditional 'P' SF's (or comparables), the classic Z41 twisty tailcap is compatible with the U2, and is another method that could help isolate the issue.

BTW if you could give us some background on the mod (~6V or ~3V?), that might also be of benefit. The more modern LED's have lower Vf's, which /shouldn't/ be an issue for the driver (especially since you're running a single LiIon) - on the other hand, the U2 has a relatively-complicated driver and a component in it could be marginal and/or failing.

Click to expand...

Unfortunately I no longer have any of the older P Surefires although I'm looking at picking one up possible as a backup light to keep in the safe. As far as the mods, I'm not really sure what to tell you. I had Nitroz upgrade it last year to I believe an XP-G2 emitter. And I am running a 3.7V/3400mAH 18650. Does that help?

U2v5 said:

The U2 is normally fitted with the Z59 tail cap. How many amps is your modded U2 pulling? The factory cap cannot reliably handle 4-5 amps... the small internal spring is too small for that current. Some later Z59s have had internal fitting problems.

My own early V59 has been bulletproof but I still installed a Z41 with a Mclicky and eliminated it as a potential problem when I installed an Oveready/TorchLab v5 triple on my first generation U2 body.

Good luck with your issue. [emoji41]

Click to expand...

I am running a 3.7V/3400mAH 18650. Is that what you are asking? And does that fall into what the "factory" tailcap can handle?

m4a1usr said:

Maybe also try running the light on a couple primaries at some point? While the U2 does typically run on a single rechargeable. It never was designed around that Vin. Might be of some use at further down the road if you continue to see the same issue your having.

Click to expand...

I want to say that I've tried that before and still had the problem but it's easy enough to verify as I have plenty of Surefire primaries laying around.

Again thanks for all the help everybody. I'm hoping to figure this out without having to send the light back to Surefire.

Re: Problem with my Surefire U2, need advice

If there is a problem with the spring in the flashlight you could short circuit the spring with small copper wire

Re: Problem with my Surefire U2, need advice

U2v5 said:

The U2 is normally fitted with the Z59 tail cap. How many amps is your modded U2 pulling? The factory cap cannot reliably handle 4-5 amps... the small internal spring is too small for that current. Some later Z59s have had internal fitting problems.

Click to expand...

The later U2's are fitted with a tailcap that is similar to the Z59 but has a matte black finish. Also, the latter U2 tailcap is slightly longer than the Z59. SF has not listed the matte black tailcap for sale separately from discussions I've read here and elsewhere.

The stock tailcaps on a late model U2 and a UM2 do have more robust springs than the one on the early U2 so the higher current from a single cell may indeed be the culprit.

Hopefully the problem will just be the tailcap, I would say that there are several solutions to that problem without sending the modded light back to SF.

JBA said:

As far as the UM2, my plan is to order one in the next couple of weeks before they are all gone.

Click to expand...

The UM2 doesn't seem to work well with 16650's but works great with RCR123A's in my experience. If you're buying the UM2 soon, you can see if the UM2 tailcap makes the U2 work properly.

Re: Problem with my Surefire U2, need advice

I modded my first gen U2 head with a XHP50 which works with that older driver.

"I had Nitroz upgrade it last year to I believe an XP-G2 emitter. And I am running a 3.7V/3400mAH 18650."

Current shouldn't be an issue with this mod assuming the tail cap is intact. Find a paper clip and bend it into a "U" shape... remove the tail cap... touch one leg of the clip to the center of the battery and the other end of the paper clip to the end of the flashlight body. If it runs without flicker on "high" replace the tail cap. Your choice of caps. [emoji6]

Re: Problem with my Surefire U2, need advice

So I have an update for the problem I was having with my U2. Yes, WAS HAVING. So I swapped out the 18650 last night with a couple of rechargeable 123's and the light and switch worked fine. Actually it worked perfectly and the light even seemed brighter than I had seen in a while. I hadn't seen my charger in a couple of weeks and I finally realized this afternoon that I had it packed away with my gear from my last camping trip. Plugged the 18650 into the charger and saw that it was nearly dead. On a whim I swapped out the 18650 that I had in my EB2 and put it in the charger and it was nearly fresh. Put it in the U2 and tried it a few times and it's fine. It's actually perfect.

Well I feel like an idiot, my "problem" was likely a very weak battery. I honestly can't remember the last time I charged that battery but it's been a while. The U2 is my favorite light but I have a few others and rotate them occasionally. With the "infrequency" that I use my lights and the capacity of the 18650, I guess I hadn't thought to charge or swap the batteries in it and I feel like an idiot now.

On a side note, and this may sound like a stupid question, but I have a habit of running my rechargeable batteries till they are nearly dead. I guess this is an old habit from when cell phones and laptops had the memory effect on the batteries and people would recommend you occasionally run them down to nearly dead before recharging it. Is this still an issue with "modern" rechargeable batteries? I really don't do that with my cell phone anymore although I still tend to do it with my laptop.

Anyway, thanks to everybody that replied back to this thread. I really appreciate all the feedback and I'm glad I didn't rush sending it back to Surefire. I have a camping trip coming up in a couple of weeks and I was worried I wouldn't have gotten it back in time.

Re: Problem with my Surefire U2, need advice

Lithium ion batteries don't have memory effect, charge as you like but don't run them to empty as that will shorten lifespan.
Best will be to charge when they drop down to 3.8V

Re: Problem with my Surefire U2, need advice

RobertMM said:

Lithium ion batteries don't have memory effect, charge as you like but don't run them to empty as that will shorten lifespan.
Best will be to charge when they drop down to 3.8V

Click to expand...

Thanks for the advice! I'll do that from now on.

Re: Problem with my Surefire U2, need advice

No worries! We would all be rich if we had a dollar [emoji385] (had to adjust the saying for today's world [emoji6]) for all the technical oversights and or missteps made.

I make a practice of topping off batteries after heavy use. Also a good practice to keep a good charger and/or voltmeter handy to check battery status.

Enjoy that U2.

[emoji41]

Re: Problem with my Surefire U2, need advice

JBA said:

So I have an update for the problem I was having with my U2. Yes, WAS HAVING. So I swapped out the 18650 last night with a couple of rechargeable 123's and the light and switch worked fine. Actually it worked perfectly and the light even seemed brighter than I had seen in a while. I hadn't seen my charger in a couple of weeks and I finally realized this afternoon that I had it packed away with my gear from my last camping trip. Plugged the 18650 into the charger and saw that it was nearly dead. On a whim I swapped out the 18650 that I had in my EB2 and put it in the charger and it was nearly fresh. Put it in the U2 and tried it a few times and it's fine. It's actually perfect.

Well I feel like an idiot, my "problem" was likely a very weak battery.

Click to expand...

Actually, great news. I've outsmarted myself a few times with flashlights. I was doing a U2 emitter mod and somehow got the cathode and anode reversed. It seems they are named differently for LED's from how they are labeled with batteries since it defines a direction of current flow. Plus is the cathode on the battery, uh, I'd better stop there lest I get it bass ackwards again. :thinking:

Anyway, from the SureFire FAQ:

My LED flashlight flickers when I turn it on — what's wrong?

• This is almost always caused by the batteries being nearly depleted. Replace the batteries.

Click to expand...

My LED flashlight does not turn on — what's wrong?

• First install fresh batteries, positive-end forward. 95% of non-working SureFire flashlights are due to dead or reversed batteries.
• If the flashlight does not turn on with fresh batteries installed, perform the "paper clip test" as follows:
  1. With the new batteries still in the light, unscrew and remove the tailcap.
  2. Using a metal object such as a paper clip or key, simultaneously touch the flat center of the exposed battery terminal and the rear metal rim of the flashlight; the flashlight should turn on.
• If the flashlight does not turn on using the paper clip test with fresh batteries installed, the problem may be dirty or greasy tailcap threads. Refer to the question below, "What parts of my flashlight need to be maintained?", paying attention to the information on cleaning.
• If the flashlight does not turn on after cleaning the threads, it may be the tailcap switch, although failures of our simple "tactical" switches are extremely rare. At this point, please call SureFire at 1-800-828-8809 and ask for Customer Service.

Click to expand...

http://www.surefire.com/faqs

I haven't had good luck with an 18650 on an EB2, did you have yours bored? Mine won't put out full power on a single cell.

Let us know how you like the UM2 if you get it.

Re: Problem with my Surefire U2, need advice

U2v5 said:

No worries! We would all be rich if we had a dollar [emoji385] (had to adjust the saying for today's world [emoji6]) for all the technical oversights and or missteps made.

I make a practice of topping off batteries after heavy use. Also a good practice to keep a good charger and/or voltmeter handy to check battery status.

Enjoy that U2.

[emoji41]

Click to expand...

Thanks! From now on, I'll be topping off the batteries regularly. What I do need is a good battery meter that's not a voltmeter. I'm OK with a voltmeter but the other members of my family are not and wouldn't use it otherwise

Vox Clamatis in Deserto said:

I haven't had good luck with an 18650 on an EB2, did you have yours bored? Mine won't put out full power on a single cell.

Let us know how you like the UM2 if you get it.

Click to expand...

I still couldn't believe that it was just a battery but looking back, it makes perfect sense. When I started the U2 in the lowest mode it would be fine until I switched it to full power and it started flickering. Oh well, lesson learned.

The 18650's have been flawless in both my U2 and my EB2. I had percisionworks (think that's his username) bore both of them out and the work was perfect. I recently bought a pair of 17670's thinking they would also work but I can only get it to work on the low mode (at least on the EB2, can't remember what it did with the U2).