Help with M6

[Justin Case]

I'm not quite clear how inserting the wrong combination of cells can result in a "loop" in the circuitry, i.e., a short. The cells are wired 3S2P. Unless you connect the MB20 + to the -, how do you short the cells?

Also, I'm not clear on your battery topology. I put a meter to the MB20 to test continuity for all of the connections. I get the following:

    MB20+
      |
   --------
  |        |
--^--    --^--
|   |    |   |
|   |    |   |
|   |    |   |
----     ----
  |        |
--^--    --^--    These two pairs of cells are lined up on either side of the + sign on the top of the MB20.
|   |    |   |
|   |    |   |
|   |    |   |
----     ----
   |______|
      |
  |--------|
--^--    --^--
|   |    |   |
|   |    |   |    These two cells are the two on top of each other, lined up under the www.surefire.com writing.
|   |    |   |
 ----    ----
   |______|
       |
     MB20-

[jamesmtl514]

I just performed the 3 battery test on the MB20.
With all 6 batteries I get a reading of 9.1 (i've used the cells for my tests in this thread)
With the 2 on top 1 on bot I get 8.8v
With 1 on top 2 on bot I get 8.8v.

I bought 3 new MN21 bulbs. Maybe It's the bulb at this point...

[DM51]

Intriguing problem... very helpful input from AOW and others above... it will be fascinating to know what caused it.

If the new bulbs don't work any better, you should give SureFire a call and send it back - they'll definitely fix it / replace it under their lifetime no-quibble warranty.

[Justin Case]

I just performed the 3 battery test on the MB20.
With all 6 batteries I get a reading of 9.1 (i've used the cells for my tests in this thread)
With the 2 on top 1 on bot I get 8.8v
With 1 on top 2 on bot I get 8.8v.

I bought 3 new MN21 bulbs. Maybe It's the bulb at this point...

If you look at the MB20 topology shown in my post #31, there are four ways to obtain 9V nominal using three cells. It's possible that the two 3-cell configurations that you tested both tested only the left side of the topology I drew (for example). If the other parallel path wasn't tested and is defective, that would explain why the cells sag so badly under load. Your MB20 gives you essentially 3S1P instead of 3S2P.

Do you have a dummy cell to use in your M4 to test the MN21?

[jamesmtl514]

I do have a dummy cell. Good idea.

I just tried the MN21 in my M4 with the dummy cell. The light output was the same as when it was in my M6.
MN60 off 3 16340 was still much brighter.

[Justin Case]

The M4 test is a 3S1P test. If it produced the same output as with your M6, I would suspect a faulty MB20, especially since you measured 4.4V under load in your M6. An MN21 draws almost 5A in an SF M6. SF123 cells probably can hold 2.0V-2.2V at a 2.5A draw. So at 5A, I can believe that the cells might sag to 1.5V each. If the MB20 were working properly and giving you a true 3S2P configuration and assuming identical banks of 3S cells as an approximation, then each bank of 3S cells should see about 2.5A draw and the total voltage under load should be closer to 6.0V-6.6V.

I would re-test the MB20 to make sure that you check both banks of 3S cells.

[DM51]

Excellent thinking, Justin

[HotWire]

Please let us know what you found out! We are all interested in your success with the M6. Right now I'm guessing you have a bad MB20.

[JNewell]

Interesting thread. I don't recall many reports of MB-20s failing.

[Kif]

Wow, a faulty MB20!?
It's time to take out all my MB20s and make sure they are good

[HotWire]

Just curious. Did you discover the problem?

[325addict]

Got an MN15 lamp assembly? Put this one in, then test again. If this one gives at least a bright WHITE beam, then most definitely your battery holder has a bad connection between the two series stacks. It then uses a 3S configuration instead of a 3S/2P configuration. Only three of the six batteries are used.
This will work fine for an MN15 lamp, that only draws 1.15A but will definitely not work for an MN21...

Another way to test it: load either an MN15 or MN20 lamp (in this stadium I woudn't use the MN21 anymore - you may be overloading the cells severely!) and take six NEW cells. Measure their open voltage, of all six. Mark the voltage on them.
Let the light run for 10 minutes, then measure all voltages again.
If three of the six batteries have an unchanged voltage, then your battery holder is DEFINITELY bad!

[jamesmtl514]

Hi everyone!
I have just received my brand new sealed MB20 from SF. I popped in fresh cells, lit it up and was underwhelmed. I lit my MN60 light beside it and it still produces a brighter, whiter beam.
I can't perform any tests or take any photos as I'm extremely limited for time lately. I just wanted to keep you guys informed and let you know that when I have more time I'll try to work this out.

THANKS!

[HotWire]

I just finished taking my M6 apart and studied all the places that allow current to pass. All the the places where contact is made should be cleaned with alcohol, rags, Q-tips, then coated with DeOxit Gold. If it's not the bulb, and not the MB20 I asked myself what else could it be? Clean the inside of the tailcap especially well. Make sure the spring is tightly fitted to the tailcap.
One of those things should help. After all that cleaning and polishing try this: Install the batteries and bulb, load the MB20 and insert it. But don't put on the tailcap yet. Take a paperclip and bridge the end of the body (a connector) to the appropriate area of the MB20. You should get full light. If you do, then the problem is in the tailcap. If it is not bright, the problem is forward of the tailcap. Good luck!

[jamesmtl514]

Thanks for the help. I'm really anxious to get this light running up to par.

[Justin Case]

I'd first get a DMM that can measure amps and check the tail current draw for the M6 with MN21. It should pull almost 5A. If the draw is more like 4.5A or less, then that explains why the output is weak (with the potential complication that your DMM might present enough resistance to drop the tail current). HotWire's suggestion to bridge the tail of the M6 is a good one. If you get full output, as determined by eye, then even if your DMM measures low, I'd say that all is else well and your tailcap is suspect.

If the DMM measures about 5A, then for whatever reason, your MN21 is "off". It is pulling the expected current but not delivering the expected lumens. Swap lamps and re-test.

If your DMM reads low and bridging also gives you weak output, then the problem could be one or more of the following:

- Bad MN21
- 123A cells can't deliver the goods
- Defective MB20 holder
- High resistance path in the remainder light (excluding the tailcap)

Did you ever test the M6 with the other MN21 lamps that you have? If all of the lamps give weak output, then the problem is probably not with the MN21.

IIRC, you've said that you have tried various sets of fresh 123A cells. I forget if these were quality cells such as Duracell or SureFire. If they were, then that possibility is also eliminated.

You've gotten a second MB20 and you still get weak output, so most likely the battery holder is not the cause.

If it is a high resistance path in the M6, I'd check/clean all metal-metal contacts, e.g., MB20 contacts, springs, bottom of the M6 "neck", and back edge of the M6 tail threads. Then re-test with the DMM and bridging. If you get full output, then add the tailcap back and re-test. If you still get full output, you're done. If output is weak again, then remove the tailcap, disassemble it, and clean it.

[jamesmtl514]

I had a few minutes to conduct some tests.
I cleaned the light, although it's just about new.
I tried all 4 of my MN21 bulbs, always the same result.
The MN60 was still whiter and brighter.
The only bulb that was brighter than the MN21 was the 11185.

[Justin Case]

I would get a DMM that can measure high current and test the current draw when using the MN21 lamp. If it is up to spec, then all is probably well and the problem is that your Mk 1 Mod 1 eyeball is uncalibrated.

[jamesmtl514]

Justin. I'm leaning towards agreeing with you. I more or less came to the same conclusion yesterday.
The other one being that my MN60 is some rare gem.
I turned on the MN60, aiming it at the wall behind my computer screen and I auto squint. It's that brignt. I waited, fired up the MN21 M6, and no squinty action. light up the MN60 right after, and I squint.
I don't know if it's the whiter beam, it's tighter profile or... some other variable. I just feel that the MN60 is much brighter.

[jayflash]

Where do you recommend buying replacement MN21 lamps and what do they sell for now?

[Snacks]

hi
was just curious to find out if the issue was sorted out. i don't have an m6 myself but i am anxiously awaiting to get one. Just wandering what the fix was for this issue.

[jamesmtl514]

I haven't had time (nor really cared to look into it as I have a lot of other throwers and as mentioned, haven't had a lot of time to play flashlights..)
I will try to make a point of cleaning it up properly and seeing if that fixes anything.

[jamesmtl514]

I didn't bother cleaning it yet. I did get the MD60 thanks to an awesome member.
it changes the light for the best. It would have been nice if it were a warmer tint, but I don't really care.

My MN60 is still a monster thrower, but the MD60 is nice and useful with it's 3+ hours runtime.

[HotWire]

I have the MD60 from Malkoff in one of my M6s. Great setup. Long runtime. The other M6 runs 3 X 17650 IMR with LF 1000 lumen IMR M6 bulb. Bright incandescent light! Both are good. At home I tend to use the incandescent M6 more because it's easy to recharge it. Away from home I take the MD60 version for the long run time.

[Justin Case]

The price/performance of the MD60 looks excellent. My main hesitation is that the 6.5V to 14V input range is overly narrow IMO. It's a shame that AW doesn't plan to make more of his turbo/sink kits.