Mountain electronics SRK Driver Issue

So I built the SRK fet v2 driver from mountain electronics and for some reason it’s not working. I checked the solder joints and all the parts are in the right spot, and the switch is wired right as far as I know (2 wires), but it’s not working. I even connected it directly to a battery and still can’t get any light out of it. Does it matter how the led wires are connected? There’s multiple led pads and ai only have a + and - connection. The leds are fine and the old driver works fine. Is the switch connected wrong?

Anyone have any experience with these drivers?


Hey Stinky,

I’d like to ask for a few more details. What type of flashlight is this going into? What type of LEDs are being used? Would you be able to post pictures - possibly of the old and new driver, the light in general, the LED MCPCB, etc.?

You got it. Thanks for replying.

The original driver is just a traditional SRK driver, 2 modes with 2 FETS for each mode. It has decent output, but I'm getting tired of just 2 modes and the PWM on the low mode is pretty bad.

The light is an SRK (one of the better quality ones) and has 4 XM-L's (I think fakes or good fakes). Let me know if you need more images.

The driver I built is the BLF SRK v2 FET driver from Mountain. I'm sure I put it together right (built drivers before).

I think I figured it out, and i got out to turn on and can switch modes, but there’s another issue taking place I can’t figure out. The switch behaves strangely. It sometimes doesn’t turn on unless you really press the switc, or it will only turn on with a fast hard press. I swapped out the switch for another one, re soldered the leads, and bypassed the switch PCB but its the same issues. Abby ideas?

Boy that's an old driver. We stopped using those FET's in 2016 or so. What's the firmware? Seems like a firmware issue now.

Fyi - A FET driver combined with those old thin aluminum non-direct thermal path MCPCB's is not a good combo. They won't take full power for long. LED's could de-solder themselves from the tremendous heat that can't escape - I've seen it, done it.

Hi and thanks for responding. Yah it’s an old one, but better than the stock driver which had bad PWM on the low mode and only 2 modes. I was hoping the replacement driver would be better, but so far it hasn’t been.

The firmware is the ‘SRK Special’ Richard offered. 7 modes. The issue kind of happened with the stock driver too, but not as bad. This was the best option cost-wise since Lexel is MIA for now (plus I could build it).

I know the stock mcpcbs won’t take the power, but I plan on replacing the XM-l’s with sst40’s on dtp boards eventually. Currently, they only pull about 6.7A total (across 4 emitters) so they aren’t being driven too hard. My plan was to get a Q8, but those are selling for $40+ still…