Went on a buying spree. Out of about three dozen different models three have switch problems that are similar but slightly different and I am not really sure if I can explain the issues properly.
You can usually confirm if it is really the switch causing this by uncrewing the tailcap and shorting the battery negative end to the body (paperclip, pliers, DDM probe, anything conductive). Once you confirm that switches are indeed broken go for replacements. Those are really cheap. About less than 5usd per 10 pack at manafont are good enough. Could ne something else tho, as 3 failing switches in a row looks like very improbable.
Some non working lights happened not to work even by using the DMM or a wire, so you would conclude that the driver is not good.Like the Shadow TC6 or the XinTD L2 will not work if they are not tightly screwed to achieve contact. In my experience dirt on the contact surface can make the light less bright or to flicker, issues that can easily be caused by the switch.
Not concluding anything yet. Just goin the easiest and probable way by use of the always working technique - elimination. There are many more causes and driver generally being the last (if it never worked correctly). Dirvers mostly dies with use/misuse not commonly being DOA. The most problems usually came from poor contact area, poor assembly and parts or poor/faling soldering and dirt.
The OP also has 3 that exibith a related problem.
Well, all three are hungry flashlights. Might be the battery PCB cutting them out for all we know. Dont know how much a xenon one draws but i suspect is a hungry one. The rest are all 3A rated emitters...
Almost all single li-ion flashlights can be checked by 2 or 3 AA batteries in series (preferably rested ni-mh).
Well I had a little time to monkey around with them this morning.
UltraFire™ WF-500 9V Xenon - I tried shorting this one out with the end cap removed - no change, used some different 18650's - nothing. I guessit's not the switch - actually the switch in this model looks quite substantial the contact is a solid rod not a spring. I therefore assume this is controller related.
UltraFire™ 504B CREE MC-E 5 - shorting this one out produced the exact same behaviour as the switch does - a split second flash. Each time I short it out it flashes once. I therefore assume this is controller related too.
KEYGOS KE-5 1300 Lumens CREE XML XM-L T6 - shorting this one out leads to normal behaviour each shrt will cycle it through it modes. There I belief this one is switch related.
Am I on the right track and is it feasible to replace the LED and controller units?
Take apart everything you can without removing solder wires, clean inspect, tighten down well. I can' tell you how many times I've had lights that did not work, but it was only because things weren't tightened down correctly. You pretty much have to assume that you will have to do some maintenance with cheap Chinese lights.
first of all I would open an RMA case on DD website for the 2 ultrafire, or thought livechat
than try to open the tailcap of the keygos from the 2 holes(best item to use are fine nose pilers or tweezers) , clean it check contacts, if you have a DMM test the continuity of the switch, If you can't or it won't work just open a PayPal/ebay claim and ask for a new switch
for the xeno maybe the lamp is burned, should be a cheap replacement, to be sure, unscrew the dropin take a dc source of 7/9v like 2 18650 in series, power supply or a torch battery of 9v and check if it turn on
do the same with the MCE LED using a dc current of 3-8v, the positive go on the internal small spring, negative is the big spring... here or the upper body is dirty or some soldering is lose or the driver is fked, btw if it won't turn on ask for a new dropin/light
have a working light is your right also if are dirty cheap!
Take care don't shortcut (specially unprotected) li-ion batteries in that operations, especially isolate the contact on the springs(movementproof) of the MCE dropin first of power it
Thanks for all the prompt suggestions - very helpful!
I will try the disassemble, inspect thing first.
The ebay seller of the Keygo was notified. I just received an email reply from them saying they are sending a replacement out immediately. I guess the margin on these is pretty significant as they didn't bat an eye - so at this point hats off to ebay seller cwtco.
DD as other people have already posted are hit and miss in the customer service department. I had already opened an RMA and they wanted videos of the malfunction - fair enough - I made two small videos but their upoad feature seems to have not been working. I emailed back on several occasions with no response. Their sign in has been down sporadically over the last week. When I finally got in I did manage to upload the videos but no response yet. Coupled with their new year has let this drag out somewhat (of which I will take partial responsibility not getting around to testing them earlier).
Funnily enough one of the other lights were backordered and they promptly sent out replacment products once I had chosen them - albeit only part of that order has arrived. I am convinced that a lot of this stuff sourced through like online fronts is drop shipped directly from the manufacturers.