Please try a bigger, spare, additional one.
But if it works now, and still works after adding another cap, what will that tell us? :~
Please report what works.
I thought you still had problems…
The blue single-FET driver works now with a 68 ohm resistor inline with the gate, it didn't work before with either the original 10 ohm resistor or wired direct to the gate with no resistor.
The 3 channel SRK driver I haven't messed with again, that one works but driving one channel at a time only.
I just tried the 3T6 driver and it works also. Yippieh!
Just cut the trace of the original PWM signal and soldered the new signal on, all modes work perfect. I tested it with a single xml2 and 4.8V.
This is an awesome concept! I've been lurking in this thread long enough... the Securitying SRK clone REALLY does some awesome output when modded! I bypassed the resistors and wow! It popped the protection circuits on my old FT Pana 2900s... That means over 5 amps drawn from each cell. I have it pulled apart now and am going to put some 16mm XM-L2s on Noctigons in.
Having the ability to add better mode selection and have low voltage warning/shutdown would be awesome, and this project would go a long way to easily (and cheaply) providing that to a lot of lights... along with massive current capability without having to stack 30 7135s and have master/slave boards. 
Yeah Werner! Been wanting to try that for some time now.
Did you just tap into the PWM out (forget which pin on the 105C) prior to the 7135's?
Yep. Just connect the Pwm signal to the right spot and bam…
Is the check already in the mail? 
Wire for the PWM-out:
None of my big pile of salvaged FETs will do anything close to what the one on the Securitying driver does. That thing is nuts.
This setup does a little under 10 amps...
It'll be used with the 3-up parts from one of the Securitying lights, and the Securitying awesome-driver will get the same treatment and will be used with the 6-up parts from the no-name 6XL2. :O
:O
I see that massive capacitor! 
The K4212 runs awesome straight from the attiny, no resistor inline, no pulldown resistor. I gotta order a batch of those things, they RAWK!
I have room for a fairly beefy toroid, should I add one between BAT+ & LED+? Would it help or hurt or do nothing?
This is one of those cool threads that hardly anyone comments on but many follow. Thank you for keeping at it and updating us all.
Another option for firmware: https://budgetlightforum.com/t/-/24491
Some real cool work you're doing here Comfy.
This is all Werner's fault, I'm just the mechanic (as usual) sticking parts together at random until something works.
His UI is just brilliant. Mode order is 0>1>2>3>4>5>0>[repeat]. But, the trick part is a short press goes forward thru the order, and a long press goes in reverse. So, from off, a short press gives you mode1, and a long press turns off. Or, from off, a long press turns on in mode5, and a short press turns off.
This one is probably not going to work with the add-on 105c. I've removed the gate drivers, going to try connecting straight to the FET's gates, but I'm going to predict it won't work. FETs are AO4468s, specs don't look great based on my limited understanding of things, which is probably why the design is so complex with the separate gate drivers and all the rest; though, why didn't they just use a FET that was a better fit? Who knows.
I've never ordered thru aliexpress before, does this look legit? Change quantity to 100 and check the updated total...
http://www.aliexpress.com/item/2SK4212-K4212-TO-252/1567621605.html
Here's the search results page, check out the crazy range of prices: http://www.aliexpress.com/wholesale?SearchText=2SK4212&catId=&initiative_id=AS_20140205055530
:~
Woohoo, never checked AE for eparts. There are some crazy prices.
I will definitely order some Tinys and some nfets from them.
The FET you found is extremely cheap.
I will first go with 10packs of tiny and to220fets I already have so that I can compare.
I also found used FETs, which got disassembled and have still some solder on the legs, lol.