Troubleshoot that threw me for a loop

I thought I would post this in case it was helpful to anyone. I was building a convoy C8+ and everything seemed to go great. When I went to turn the light on nothing happened. I was afraid I had shorted something by accident and killed the FET, like I had once before. I had the insulator in place though and had taped the reflector with Kapton tape. I should have checked for a short before turning the light on but I didn’t. “Lesson learned” I thought.
Figuring I knew the problem, I grabbed another driver and put it in (still not having checked for a short (I’m a slow learner (and a fan of parentheses))). I checked for a short and everything looked good. Light works (and there was much rejoicing).

I messed around with the gasket and focus a little. Checked the light and… nothing. Uh oh! I checked for a short again and everything looked good. So, I put the light together and it worked again. Not knowing what the previous issue was, I doublechecked the threads, looked everything over, and tightened everything up… and it stops working again. It alternated between working and not working while I tried to find the problem and disassembled and reassembled. After a lot of head scratching, it turns out I think the machining for the pocket for the driver was a little off. I realized if I pushed on the spring or driver real hard, I lost connection between the retaining ring and the driver. So, if everything was assembled tightly, the battery would push the driver up and disconnect it. But when taken apart everything looked fine. If everything was a little loose though (particularly the head), then it didn’t press hard enough to disconnect it. Part of what contributed to my confusion was I never got any flickering or other signs of poor ground connection. It was either 100% functional or 0%. Additionally, the retaining ring was nice and tight with the driver looking centered and feeling snug.

In the end, no matter how tight I tried to get the retaining ring, I couldn’t get a solid connection. That’s why I wondered if the pocket was too deep, or maybe the threading had a burr or something which prevented it from getting as tight as it should. So, I put a few solder blobs in there and had no troubles since.

There are some boards made for our normal drivers that are thinner than OEM, for these you have to put a few solder blobs around the ground ring so the retaining ring can hold it down firmly and make solid contact. Mountain Electronics sells these thinner boards and the plus is that the copper traces are heavier. So it’s worth having to fine tune fitment. :wink:

I have been building with FET drivers since Comfychair first proposed the 07N02 on a Qlite, I’ve never killed an FET and I’ve had my share of mistakes happen…

What DB said. Add a bit of solder to your driver ground ring, then tighten the retaining ring down. The difference between 1.6mm and 1.2mm may only be .4, but its a big enough difference to cause issues!

The threads for the retaining ring bottom out short of the ring making solid contact with the thinner board. You can really see the performance go up with a solid ground, for these thin boards you just have to take that extra little step…

My problem last night was throwing a moonlight special into an S2+ with Kiriba-Ru's solid copper triple pill. The double-sided driver didn't have any room for the retaining ring to hold it down... I fiddled with it for ten minutes and then just soldered it in at four spots around the ground ring. It's a gift light, so no further modding, and I made sure to test it thoroughly. (Red S2+ with 4000k SST20 CRI95 if anyone cares). Also the shortest I've ever made the LED wires on any light... there was only 1mm of slack, if that, once everything was soldered in place. Would not want to re-open that one.

LOL, I always make my builds with the wires as short as possible. I put the wires on the driver, install the driver, cut the wires off where they fit… no slack.

Thanks for the comments guys. I did realize that some of the mtn boards were 1.2mm instead of 1.6mm. I didn’t know that was prone to cause problems though. I am not an experienced modder but I have built about 5 of these lights and not really had an issue before. Maybe I got some of the newer boards for the other ones or just got lucky somehow. But either way this one was a no-go. I should have included that it could have been due to a thin board. I’ll probably start soldering most of the drivers in place now as they are usually for family members or friends and I have a decent soldering iron now.

The one board that I thought/think I may have killed the FET on I contacted Richard about. He, like you Dale, indicated that the FET’s usually are not the first to go and was probably fine. I did, per his recommendation, check the light again without the short and still had nothing. Additionally I proceeded to purchase a FET from Richard and after using it to replace the one on my board, got the light working. It certainly is possible I had the same issue as last night and wrongly blamed the FET. When I reinstalled the driver with the new FET it did go in the same host and seem to work fine then. That was why I felt the short and the FET were the problem. I think I have that FET still. Maybe I’ll try putting it on another board and see what happens.

I have had to solder double-sided drivers to the regular S2+ pills. I haven’t messed with Kiriba-Ru’s pills though. I’d like to though.