Mine is fine so far (crossing fingers)
I saw a thread on the “other side” where someone else had the same issue, but I don’t think it’s a pervasive problem.
yah google did lead me to “the other side” and i saw his photos. anyways il put an xml in there. kind of an upgrade to tk41 
status
will let you know how it goes with photos and beamshots etc next couple of weeks .ordered driver and a xml t6 just now from china The land of the free … Ooops i meant cree
How about a driver such as a B3flex from taskled? I know that it uses a momentary switch for changing modes etc.
Ive never seen a tk40, but from the photos it looks like the wire that is screwed to the housing is the permanent gnd. The centre contact on the reverse is pos and the outer ring around this is the momentary gnd contact used for the modes.
Of course i could be wrong…….but if im correct the taskled driver will work!
Woody
thanks woody ,this looks like a high end driver ! Costs $35 !
i ordered these 2 drivers from lightmall . They should be here in 2 weeks!
http://www.lightmalls.com/super-output-ssc-p7-led-driver-board-low-high-middle-5-5v-15v-2
lets see if they work
Since Dr. Jone’s drivers are AMC based it will not work in the TK40 unless you wire the battery holder for parallel instead of series. Perhaps you can find a way to use a regular driver by finding a way to isolate the negative ring on the driver and replace the side switch with a momentary off switch. Then you can wire from the negative ring to the switch and back to the driver. Then you can keep the side switch mode changes without a special driver. Sorry I didn’t answer your PM sooner but I was waiting to see what you found in the driver. I didn’t see this post until now. 
johnny , when you didnt reply i thought you were in the operating room getting your knee repaired !!
heres my plan !
bought these items. scream at me if im doing somthing dumb
Be warned that is not a 17mm driver, it's 19mm.
meaning??? :cry:
driver details
Details
15V Super Output SSC P7/Cree XM-L LED Driver Circuit Board (Low/High/Middle,5.5V~15V)
Fit fot the Cree XM-L,SSC P7 emitter
- Current regulated at 3.0A
- Input voltage 5.5V-15V, (no more than 12V would be the best option for protection of LED board according to accurate test)
- Buck Voltage Current Regulated circuit
- Gives 1+ hour current regulated (3.0A) output with four Eneloop AA
- Gives 3+ hours current regulated (3.0A) output with two protected 18650 batteries
—Gives 90~95 efficient output
- Measures 19mm in diameter, and 8mm in height
- Multi-Mode: Low(5)/High(100)/Middle(35%)
- Designed for SSC P7,Cree XM-L LED for maximum output 300lumen-1200lumens
- 1xLED+, 1xLED-
- Prewired, ready to use
and the tk40 battery pack has 8 AA battries
i scrapped off all the circuits from the driver board … drilled hole untill the positive got exposed ….
1-now will place the new driver on top on old driver…
2- solder the positive …
3-send positive and negative wire to the led….
4-solder a wire from new driver negative input to body …
5- attached a new forward clicky switch …
Note : the Old drive is only needed as compartment cover and provide the positive contact from the battery pack . all circuits are removed . Its a just a flat board now
Very interesting thread. I have a tk40 that I haven't used in about a year and a half at least. It's actually one of my best dust collectors. 
I'll have to dig it out and see if it still works. 
lolzz… its a great light isnt it! mine was used to search for a friend who died while on a fishing trip back in my homeland fiji ioslands)! so im attached to it emotionally. and will give my best to make it at least 900 lumen (more bight then its elder brother tk41 
)
The diameter of the driver is 19mm, this can be a problem as a lot of lights use 17mm drivers.
What happened to the TK40?
[quote=Rusty Joe]
What happened to the TK40?[/qu
the light ouput went around 200 lumens at turbo. the mce led went dark brown colour.
its been used a lot…probably few hundred hours
Old driver is 35 mm while new one is 19mm. so its needed For proper fit n finish
the diameter of the tk40s driver is 35mm…and the new 19 mm driver i purchased was made for an xml …with a 5.5to15 volts input :~
and if the input voltage in too low for the driver ((((it does say on the website that this driver - Gives 1+ hour current regulated (3.0A) output with four Eneloop AA so i will scream in chinese if it doesnt work |( )))…il modify battery carrier and place all 8 bateries in series resulting in 10 volts!
or buy another driver that accepts around 5 volts J)
Sorry to hear about your friend Shaq. Now I see why you want to keep it in good working condition....I would too.
It is a great light but just a bit too big for everyday/night use. I've been using my smaller E1320 lights around the house lately but I will pull out the old tk40, dust it off and play with it as soon as it gets dark. 
[quote=Shaquille]
That sucks. Fenix is supposed to be top quality. How did you like the output when it was new? You know you can send it in and have it repaired, right? Modding it would take out the originality of the light you bought. Although, not modding would take out the challenge of practicing flashaholism.
[quote=Rusty Joe]
i emailed fenix and the dealer but reponse wasnt what i expected.i hate it when i have to be the begger . the light is top quality.glass is still shiny like new.and its been used lots!!! . i decided to mod it . Can you imagine what the beam profile would be from an xml ! the op reflector and glass are of very good quality. Its a huge head so im expecting a massive floody beam. The new drive has a Low(5)/High(100)/Middle(35%) I prefer less then 3 modes on my flashlight. the output was amazing back few years ago but now my skyray king (thats half its price) beats it pants down …2000 lumens from a 50 dollar light vers 630 lumens from a $130 light…