I would personally recommend that you send it back. I know it stinks, but Sunwayman lights are too nice and expensive to accept a major defect. It seems that Sunwayman’s quality control isn’t very good at all. There are quite a few reports here on BLF, and I personally had a defective V10R. I sent it back to FastTech and received a very nice functioning replacement today. Once you get a good Sunwayman, they really are nice lights, and worth the price.
Do I send it back to sunwayman or the dealer I bought it from? I contacted the seller but didn’t get any respond yet
I’d wait to see what the seller says.
I just discovered this in Relic's review (check out the second bullet):
Lockout Mode:
- To lockout the light, while on or off, press and hold both buttons for 1.5 seconds. The light will flash very quickly and turn off. Subsequent button presses have no effect.
- To exit lockout, press and hold both buttons for 1.5 seconds. The light will exit lockout and turn on.
Physical lockout can also be achieved by loosening the body about 1/8th of a turn. <-- Is the way I have been doing it. Now that I know the above, I will be using that method. I bet I have been accidentally doing the above from time to time.
My vote is contact the seller. Any good seller should have no problem taking care of a DOA light.
I’m definitely buying a D40A. Looks like a fantastic light.
Got my D40 from Illumination Supply last week. So far it's been flawless. Sorry to hear you're having problems with yours..
so i thought it was my batteries that caused the problem, so i went to costco and picked up a new set of eneloops, i fully charged 4 of them, put it in the lights and bam it worked!!! but only for 1 minute and the blinking aviation mode happened again and i couldn’t access the power and mode buttons anymore, i seriously do not know what’s wrong. i hope i can fix it myself so i do not have to wait for weeks again.
Are you sure you're not accidentally be pressing both buttons at the same time like described in Post 9 above?
i do know about the lockout function, but in this case, i am unable to use the power and mode buttons, i pressed both of them for 2, 3 and up to 10 seconds to see if i accidentally locked it, but nothing changed, i wonder if the blinky aviation mode is a low battery indicator? but i can’t seem to find that information anywhere, i just went to borrow a lacrosse charger from my brother and charging the batteries let’s see if miracles happen lol
Looks like the driver is easy to access with just 3 screws. You may want to peak at it to see if there is a piece of plastic or something between the driver and the driver cover/contact plate. Maybe clean where driver and the cover/contact plate make contact with alcohol. Something could be there creating high resistance which would eat up voltage from the cells.
EDIT: Here are some good pics. About 17 pictures down or so:
It sounds like as soon as he puts the cell carrier in, twists the tailcap on, the moment it makes full contact with the head, it just starts slowly blinking w/o him pressing any buttons.
Is there a low voltage signal/flash as well as the lit indicator? Its as if the current is neutalized (a short?) which is why it works for a bit with loops since they have more current to give…no?
Perhaps not a good idea to open up the head/driver if he plans on returning it.
So the missing wrapper on ur cell, he supfire m6 being missing and now this…. 
Sucks bro…
Here you can see my problem with Sunwayman d40a xm-l2,
I send the light to dealer and he will send me a new one after contact with Sunwayman.
thanks bro, its ease my pain knowing someone actually care. blf is great
Looks like jpil had the same problem as you except his went on in low instead of the beacon. You have a whacky driver I guess. Send the seller a vid and tell them you have a defective unit. Sucks but more waiting for you. 
Has the replacement light arrived yet?
yes it did, when i was waiting for the replacement, i took the flashlight apart, i just switch the connecter around, from the switch to the driver, somehow magic happened and it worked till now, so i paid the seller for the second one, which he/she did give me a discount. now i have two sunwayman d40a 
"and it worked till now," Does that mean it's not working now?
Glad to hear you have at least one working. I thought the light was ok at first, but it really grew on me over time.
I continue to be impressed by my D40A.
My bad, the original one is still working perfectly fine.
Normally for a popular new flashlight there’s a subset of people who hate it. The D40A seems universally liked.