I bought this SRK from an ebay seller, and right from the start it acted flaky. Initially, it wasn’t as bright as I had hoped, but after about a minute the output was greatly reduced, but all modes still worked. I had feeling it was either a bad trace or solder joint on the driver board, or the MOSFET was NG. I took it apart and sure enough the LEDs were good. Here is a picture of the driver\
The first thing I noticed was the MOSFET, the leads looked like they were light on solder, so I added more. No change. I visually checked the other components, they looked good, good joints etc.
So I pulled the MOSFET and bench tested it with a DMM. I was OK, so far as that test showed, so I re-installed it.
Same problem. Because all modes work, but at greatly reduced brightness I figured it is a current limiting issue. Those 4 large “0” resistors are jumpers right? No current limiting there. To be sure, I touched my iron to the solder joint of one of them to make sure there wasn’t an invisible bad solder joint. I have seen PLENTY of those over the years. I didn’t expect much as there are 2 sets of 2 in parallel, both would have to be bad. When I did, the light got much brighter. When I removed the iron, it dimmed. Back and forth I went, each time I heated it up, the light went to full brightness, each time I took it off, it dimmed. Anyway, to make a long story short, it turns out that each of the “0” resistors measure at about 20 ohms! Could it be that they “blew” into a 20 ohm state? I jumped them all with wires and rewired the LEDs with better wire and now the light is fine!