Help me figure out a weird issue with this light?

A couple of years back my brother purchased a Quark AA² Turbo to take with him on his deployment to Afghanistan. He ended up having to use Alkalines in it at some point and they leaked. 4Sevens isn't willing to cover it under the warranty (which is unfortunate but I understand). I was able to remove the batteries and clean out the light. The head is fine, none of the leaking appears to have made it up there.

Here is the part where I'm stumped. When I put fresh batteries in there and try to use the light, it won't turn on. If I replace the tail cap with something conductive, a coin, a piece of foil, or whatever the light works as it should. Simple enough you might say, the tail cap is bad. I thought so too and ordered a replacement. The replacement still doesn't work. I have found that if I just hold the tail cap on the end without screwing it in place at all then the light comes on (just like my earlier tests) but as soon as I screw it on, it stops working. It probably doesn't make a difference but both tail caps are the tactical style.

Any ideas?

Did you clean the threads/contacts well?

As mentioned, clean the contacts (The shiny, flat parts on the ends of the tube).

Tighten the tailcap contact ring to see if this helps.

Check that the positive contact is in good shape (It may need pressure to make contact due to the alkaline damage).

Also make sure that the retaining ring for the clip is tightened all the way down. If it's loose, you won't be able to tighten the tailcap all the way down.

I did check the retaining ring and that didn't make a difference. The positive contact seemed to be in good shape. I forget what I used to clean the contacts with initially but I will certainly try again. What would you guys recommend for cleaning the threads and contacts?

Avatar28 said:

I did check the retaining ring and that didn't make a difference. The positive contact seemed to be in good shape. I forget what I used to clean the contacts with initially but I will certainly try again. What would you guys recommend for cleaning the threads and contacts?

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De-Oxit Gold works wonders. Confirm that it is okay to use near aluminum threads, just in case. If you don't want to buy things, gently rub the contact points (Flat ends of battery tube, positive contact, spring top, and copper-colored ring on PCB; not so much the threads) with a pencil eraser. You can then clean the eraser by rubbing it on a soft cloth.

Thanks. I'd ended up emailing 4sevens again. Zack over there suggested cleaning everything and lightly sanding the ends of the tube where it should be bare aluminum. I will try all of your suggestions and see where it gets me.

Try pushing the battery into the compartment (towards the head) at the same time as you bridge the -ve contact of the battery with the flashlight body (ie using it without a tailcap). This will replicate the pressure the tailcap spring exerts on the light engine in the head. I'm thinking there might be a short/break in there that only causes trouble when the l.e. is under pressure.

marshall from going gear just posted a video to address your exact problem, Check it out

http://www.youtube.com/watch?v=yRysLmy44Wk&feature=g-all-u&context=G24a2368FAAAAAAAAAAA

I've had similar problems from time to time with other lights. If you bridge the battery and body and get light it's the tailcap. As mentioned, clean everything, tighten the retaining ring. If that does not work replace the switch with a generic switch from Shining Beam or ...... You might have to buy a few switches to find one that will fit and work. Sometimes you can take switches apart and clean/lubricate them. De Ox It is wonderful stuff. Maybe you could buy another Quark switch....