BLF Q8 does not power down completely


since yesterday my trusty Q8 does not power down anymore. The LEDs keep glowing. This problem has not occurred before. It is reproduceable with batteries and a bench power supply.
I already reflashed the light with narsilm and also anduril, but both firmwares have the same problem.
Has anyone any idea how to fix this?

If there is a small short between the LED negative and ground the LEDs might glow in e-switch lights even though they are turned off. I have had this happen a couple times and I think the short was located at the solder pads of the LED footprint. Did the light get very hot before this behavior started? I’ve observed that can change the effective resistance of the short, possible from flux residue or something.

Well there’s an idea. I’ll reflow the SBT on my FT03S.

Thanks for the suggestion. The light did not get particularly hot, but neverless, i connected two different LEDs to the driver just to check. Unfortunatelly the problem persists.

You mean you disconnected the 4 LEDs from the driver before connecting your test LEDs to the driver, and the LEDs still glowed? If so that would seem to rule out the short at the LEDs. A small short at the FET (or 7135s if the driver uses them) could also cause the glowing behavior.

Yes, i desoldered the leads to the original LEDs and connected the driver then to some different LEDs. After your suggestion i also removed the FET and the 7135, cleaned the pads, and soldered them back on, but the problem remains.

I guess there could be some small leakage internal to the FET or 7135 chip if they became defective? You could assemble the light with the FET or 7135 chip left out to help troubleshoot.

I appreciate you doing the work so quickly to check my suggestions. We are definitely not the only people to have the glowing LED problem so it will be interesting to find out where the problem can lie.

A bad 7135 chip can cause this glow. I suggest desoldering the 7135 and replacing it with a fresh one.

Yeah, a “leaky” pass element is the usual culprit.

A 7135 can leak some parasitic current if bad. A “leaky” FET similarly (mostly the bigger beefier ones), and/or the gate can float a bit high and cause leakage and might need a pulldown resistor.

Forgot which light, but when people were swapping come-with FETs for bigger ones, that problem seemed to spring up out of nowhere.

That did the trick! I didn’t think a 7135 could just “fail” like this from one day to the other.
Thanks everyone for the quick help!

no idea what exactly this all was, but a fascinating read!

What a site !!