FW3A Troubleshooting / FAQ

Yes that was my point, the gap…
How it should be.

The bigger question is if the trace burned first due to some other reason and the spring was nearby so they got melted together. Or was there current from the spring to the trace?

Negative current from the battery is already flowing up to the driver at all times (same for positive current) so I’m having trouble unstanding why the trace burned.

This trace basically connects a very weak positive signal from the MCU down the inner tube and across this trace. When you push the button this weak positive signal gets grounded through the vias and to the spring.

So if the spring shorted the trace it should be no different than holding down the button. I’m pretty sure the MCU limits the signal current to like milliamps.

I can’t think of any reason that trace would carry high current, high enough to burn it. The spring touching it should not cause a high current flow.

In these 2 pic’s it looks like the spring is only secured/soldered on one of the 3 pads? The other 2 pads look untouched?

Looking at the 5 I have, all of them have an air gap over the signal tube trace with the spring sitting on the 3 solder pads.

Just an observation…

That appears to be the fault in the one i had short, while the edge of the spring was not directly on the trace, as seen in the photo the spring edge was roughly 110 degrees at roughly 2 o’clock on the board, so the spring was directly resting on the trace. Also i did notice as seen in that photo the spring is only soldered to one of the three solder points, and i could lift the spring up off the board a little as it only had one weak solder point. As seen in the second photo, you can see where the two other solder points were not soldered to the spring at all.

lol i had posted that exact thing just as you did. indeed, it was only soldered in one small spot on one of the pads, the other two were not.

Resistance, the spring only held or making contact on one solder pad. Maybe the srping got hot enough to burn thru the damaged masking after the fall, and the heat from resistance burn the trace? Kind of strange really, unless the driver shifted and made some kind of short? It is strange indeed…

So the bottom end of your spring is soldered at the pad nearest the ‘F’ in the FW3A label? That allows for the maximum air gap.

Upon closer inspection, my spring has solder on all three pads, but only one is making what I’d consider a ‘good’ connection. The other two look a bit cold and could use some more solder. I’ll touch everything up when I rotate my spring.

Yours looks like the position of mine. If they had placed the spring cut-end on the 7 o’clock solder pad, then there would be a good 1/2 mm or more gap over that narrow trace. Its an easy fix to rotate the spring as fortunately the switch board is easy to remove from the tail cap.

Oh, great! :stuck_out_tongue:

I wonder if Lumintop would consider taking the time to purposely install all the springs in that position.

BTW, I measured the gap on mine and it’s 1 mm at the widest point.

absolutely thrilling for those of us who are clueless about what you speak of. NOW I feel like I shouldn’t handle my flashlight like I normally do. Sheesh!

You guys had me worried a bit with this discussion because the end of my spring sits directly on top of the trace that shorted and I have knocked the light off a 2 drawer file cabinet where it lives no less than a dozen times (likely an underestimate) . Yes I am that clumsy.

Yes there is only one good solder pad holding the spring. :open_mouth: But fortunately it is the one to the left of the trace which happens to be holding the end of the spring slightly above the surface and I expect that makes all the difference

@ shirnask …. Those are good clear pictures showing the end of the spring. Thanks for posting! :+1:
That should help clear up some of the confusion that was mentioned earlier. :beer:

So the spring is carrying high current and should never touch the signal trace which only carries low current.?

The spring should never be able to bang into the trace hard enough to break through the mask on top of the trace and cause a short

Those are good photos of the example of the spring end being in a place where if impacted enough could “dig through” the coating” and short through the trace. but in your case as you mentioned, they soldered it with the spring just off the board surface, making your’s lucky to probably not short in that spot. When min fell, it landed tail-cap down hard on a hardwood floor, making the battery slam down on the spring hard enough to short the trace.

Not really.

The spring should only carry high current when the light is on a very high brightness level.

The trace only carries low current.

From what I can figure out, if the spring touches the trace it simply bypasses the switch so the light turns on. There should be no high current flowing through there.

There should be no way you’d have high current due to a short. The battery positive goes straight from the battery end to the leds and stops at the driver FET and 7135 current regulators. So there is no positive battery power in the tail except for the tiny trace signal coming from the MCU. This current is regulated at a very low level though since pushing the button shorts it to ground and no high current flows then.

When the light turns on Turbo you get a lot of current (12A) go through the spring to the 3 solder pads. Then it goes through vias to the backside of the pcb. That whole backside is negative except for the small circle pad under the metal switch dome.

So if the spring touches the trace, high current will flow through the vias like normal, but I don’t see how high current would want to flow through the trace. That trace doesn’t go anywhere but through the inner tube to the MCU pin.

Maybe the spring got hot from only being soldered in one spot instead of 3 and the heat transfered to the trace? IDK, I’m stuck on how it could happen.

Maybe the current flowed through both the vias and the skinny trace and the vias can handle much heavier loads so the trace heated up?

:stuck_out_tongue: I stand corrected. Yikes!

Push the spring down hard, see if it flexes at all.

/\ … If it does, slide a small piece of plastic milk carton under it & forget it. :wink: