The transition from design to production is a problem in purchasing flashlights from new makers or manufacturers.
Mine does not show the problems you mentioned (I did not examine the driver), but mine might have come from an older production run.
I hope you have contacted Manker.
I got my U21 last week. Same driver as KB. Tail threads well lubed. Other end bone dry zero lube. No crud but same off center led. Centered easily. Good solder connections. Excess thermal paste. No twist noticed when reassemble. Hot spot very well defined at all. Noticed better after TLC. Will also compare with the stock X1. Thanks KB for telling what to look for:THUMBS-UP:
Mine was an engineering prototype, they sent me not realizing til after it went out, so driver probably somewhat different.
I was tempted to get this light awhile back if issues are arising glad I didn’t. I can’t just easily mod and fix a light like most of y’all can. If I spend $70 on a light I expect it to be perfect. Not need led centering. Or wires jammed in about to short like the cometa they made.
The light still picks my interest though being 1 cell xhp 35. I wish they would have a true turbo with no step down. I end up sending my stock lights with it for modding. I can’t stand a turbo step down. I have it on turbo for a reason. If it gets to hot or I’m done I’ll step it down. I could see mayne a temputare step down as a safety measure 80c+ but not timed. Or at least let the user have different mode groups with or without it. Hopefully more manufactures like convoy or thorfire make a light like this. At a cheaper price point their known for
Mine doesn't turn on looks like a switch failure
Hello. I bought it 6 months ago from gearbest and use it only 10-15 minutes. It was perfect. Yesterday get ready for camp but the light didn’t work. I prepared a video for it. *Battery is OK. *Switch and under switch leds are OK. (with usb charging port) *XHP35 hi main led is OK. (with usb charging port) *Tailcap is OK. *4.22 volt is OK with usb charging port. but cannot charge battery. I think it imagines battery is fully charged * I tried to loosen body tube from head but it is imposible. Can you say what is it about. Driver or what? Video- - YouTube
Great review and photos as always Tom e ,I really love the mod you did on mine it is now my ace
.I was because of this initial reviews i bought this light.
Here is mine bought from Geabest faulty switch after 6 months. https://youtu.be/Mrw7tg5LhVw
@ Tom E ,
I got my Manker U21 about a week ago , and after I readed your post , something seemed to be not right..., I measured mine ( Fluke , with short and thick probes , IMR26650/4200mA/40A , from Nitecore ) , and my readings , especially on high and turbo are different.., as follow :
Low : 0.02A
Medium 1 : 0.27A
Medium 2 : 0.65A
High : 1.30A (!)
Turbo: 3.70A(!)
So , I decided to do some math , to see what is going on...
Your driver :
P output : 12V X 1.1A = 13.2 W
P input : 4.2V X 5.44A = 22.8W (!!!)
The efficiency of the driver = around 58% (!!!) .., even the worse boost drivers I worked with , doesn't have such low efficiency !!!...
My driver :
Poutput : 12V X 1.1A = 13.2W
Pinput : 4.2V X 3.7A =15.54W (!!!)
The efficiency =about 85% , this is an acceptable efficiency ( I've seen and tested boost drivers with 95%...!)
I don't think that Manker , as many other manufacturers , will exceed the max current to the led ( in our case , for XPH35 HI , is 1050mA..!. I took in my calculation 1.1A ...) so , or your measurements are wrong , or your sample has one of the worst boost drivers I ever seen...no pun intended !
Anyway , that 5.44A to your tail is far too much , and due to the efficiency of this kind of led you should have more than 1800Lm at the output , including the loses...
Sorry , I did not intend to disturb you , but , as I said before , something is NOT right...
I believe I read the early samples of this light were giving 1.5 amps to the led which would be 18-19 watts and so just a bit less efficiency than your numbers. Although there is some estimating in both cases here.
For some of the samples ( reviews on " Fonarevka " , "Forolinternas" , Selfbuilt Review and some others...), the measurements for turbo mode are in the range of 5-6 Amps , BUT the run times in this mode are consistently OVER an hour ( 1h and 21 min , 1h and 15 min...) with 18650 batteries , of 2900-3500mAh , that is leading me to the conclusion that 5-6 Amps is NOT a correct value ( just do the math...)
More interesting is that , on my sample I did not noticed a step down from turbo after 3-4 minutes , as most of the reviewers...!
Also , the temperature of the body , measured after 30 minutes was under 50 degrees Celsius so , the temperature was under the kicking point !!!
To be sure , I tested the light with different types of 26650 batteres ( Liitokala , KeepPower and Soshine ) , fully charged ant tested before for 10A discharge , with low voltage sag at this current ..,and the results were consistently the same ...! Current on turbo around 3.7 A and the running times between 72 and 85 minutes , depending on the capacity of each battery ( 4200-5200mAh )...More than that , on the last test , at every 3 minutes I performed an " off-on" of the light , to be sure that is in turbo mode , all the time ! Making the math again , is clear that the current SHOULD be 3-4 Amps , in order to have more than an hour in turbo . If the current was about 6 Amps , how come the running time is over 1 hour , with an 4200 mAh battery ??????!!! . You see what I mean ?
What is going on here ? My light is so different , even if the driver is marked as all I've seen ( Manker DL046)...
I'm sure of all my tests and my measure instruments ( because I tested them on other flash lights that I have , is nothing wrong ...).
For sure , I do not have a " super " sample , somewhere the numbers are wrong , and not mine... the math is giving me the right to say so...
By the way , I measured the led current , is a constant 1.09 A , on turbo !!!
From now on I will keep away from Manker Lights. Hope my Manker T01 doesn't have a problem as well.
What is it exactly that you are trying to determine? That your light is different than the samples? Yes, it has already been known that manker made a change sometime early on. Or that the early reviewers were miscalculating? If so, early numbers were fairly consistent, output is higher and more power to led than later production with a driver prone to fail. And those early reviewers, like tom and mitko, also reviewed the later production models. So, are you seeing something different or just pointing out what has been known?
Yes LR , I 'm seeing something different and I do NOT pointing out what has been known !...I have no idea what batch this particular light is , I bought it from a store , here , in my town , bright new in the original box.., the seller told me that was ordered 2 months ago direct from Banggood , for a buyer that never claimed it...Long story short, I think that I missed the part where Manker changed the drivers for this one ( this is a new information for me ...) , but if so , I have to say that this "new" one , is performing much better !...What is the use of more lumens if the reliability is compromised ?
Thanks for your information , and I apologize if I was out of topic...
Ok, this must be what you see. The change was frustrating to many as Manker never updated their information to reflect the lower output but it is still a nice light with a very efficient driver as you noted. Some of us have been modifying them for more output by changing the sense resistor value. When this is done, one can achieve numbers like the early reports but not many have reported whether or not their modded lights have been reliable. Some however, have modded with added r100 resistor and reported a boost without problems.
That is a quick summary of the story at least. Actually, right now I have some beefed up diodes on the way and my intent is to replace the stock diode, mod with r50, pot the driver, and see how it goes. 
Thanks LR , this must be the explanation...Your approach for modding U21 seems to be very... "courageous" ,but what the heck , we do this all the time , right ?
Unfortunately , I wasn't able to budge the battery tube from the driver side .., I've tried everything , from brute force , boiling in zip-lock bag , freezing , vice and strong straps !!! .., is not moving !!! I opened a lot of stubborn lights in my life , but this one doesn't want to be seen from inside ..! I'll persevere with some more "barbaric " methods , the gas torch is my last resort...( hope that this light hear what I'm saying here, and tame itself...)
You said " mod with r50 " ... doesn't seem to be much (!) , maybe you mean to say "r050" , and THAT is an other story , to an other level..!!!!! Must be r050 if you decided to change the diode , isn't it ?
Anyway , thanks again for your information , and good luck with this .., maybe a new post with the results.., much obliged for this ...
Oh yes. My bad. I meant to say r050.