FW3A Troubleshooting / FAQ

Why not just use wood , find a bit of dowel of the right diameter then cut it to length.

That would work nicely. :+1:

A fellow glue guy. :+1: I like Pro Poxy myself. Dries like steel in 20 minutes.


Here’s a FAQ copied from the main FW3A thread:

That’s the main symptom of a switch tube contact issue. I haven’t seen it happen on my production sample, but I know the issue well from seeing it on earlier prototypes.

Loosen the tail a bit, loosen the head, then tighten the tail as much as you can, then tighten the head. The issue should go away.

If the issue returns, loosen the head, tighten the tail again as much as you can, then tighten the head. Try to keep the tail as tight as possible. And always tighten it tail-first.

would be a good idea if the thread owner can add the "did you already try (to switch it off and on again)" information in the OP


  1. unscrew the head
  2. do you see the positive end of the cell? (which can be max. 67mm)
  3. measure the cell voltage (must be above 3.5V)
  4. watch this video to learn how the tailcap is assembled : https://youtu.be/D1dfPeO07bM
  5. unscrew and disassemble your tailcap
  6. Inspect every part for damage (contact areas are clean? )
  7. assemble and tighten the tailcap first!
  8. insert the cell
  9. mount the head
  10. if it's still dead/funny follow ToyKeepers steps to troubleshoot the firmware...

I was kinda hoping someone would volunteer to collect the useful info into one post, so it can be linked from the OP.

I’ll do it. :+1:

In the morning…. :wink:


Try one of the single circle LEGO pieces. It looks to be about the right size, maybe a little small. I can get an actual part number if you need.

Specifically a 1x1 plate
ID: 4633691/6141

Not quite.

The circle on top of a lego brick is 4.8 mm across.

The FW3A nub is 2.0 mm across.

If you’ve ever had coarse-grain sugar, like “raw” or turbinado brown sugar, the FW3A nub is about the size of one grain of sugar. Maybe a relatively large grain, but still. It’s basically the size of a single cake sprinkle.

Seems like a piece of a plastic welding rod would be suitable here. Harbor Freighr used to sell this pack but couldn’t find it on their website any mor. Is it possible for that store to go downhill?

I am thinking about this nubbin issue, (piston) while I do not have a light yet after only reviewing images and M4D M4X ’s video, would it be easier or more practical to bond a suitable object to the dome of the switch?

More thinking and experimentation would be required. the dome probably deflects or deforms which would cause a distortion and break the bond. I don’t know I don’t one have to futz with.

The switch to me appears to be metallic in fact it looks a dome of a membrane switch.

To replace the nubbin itself Amazon offers these items Plugs
I can image cutting one of the smaller ones 1/16 inch diameter to size these plugs are tapered so the size could be improvised. Then use some RTV to bond it in place.
I am just thinking out load here so I really don’t know if this would work.

This nubbin issue is really bothering me I don’t know if I will buy a light because of it. It is IMO a manufacturing flaw the design is clear I think it was executed improperly.

My 2 cents

Also a suggestion for the adhesive - Pliobond. It’s a very tacky contact cement that resists solvents. I’ve been using it when repairing old cameras, gluing everything from light seals to rubber bumpers to the old peeling leatherette on the bodies. If it’s improperly placed, once the carrier solvent evaporates it peels away with no residue.


Just hold onto your nubbin.

Silicone comes unstuck to easily. Goop much more tenacious bond and remains flexible. Maybe this whole thing is a non issue if the switch is never taken apart. Has anyone’s come un-nubbined otherwise?

If the switch isn’t disassembled I don’t think there is room for that to happen?

It would be nice to know the materials being used so one could use an appropriate adhesive.
If mine gives me issues I might try Bison’s Plastic Adhesive since it’s what I have.
But I don’t have high hopes for it working since I’ve a suspicion that the big part might be PP which the Bison isn’t suitable for.
In case someone wonders, that Bison adhesive is just a mix of PVC and solvents so it sort of “melts” the parts together.

Unfortunately I don’t have a very good soldering station so can’t really test the softening or melting point of the plastic accurately.

Yep… :+1:
If you don’t happen to have any Silicon laying around, you can use one of the below if you happen to have them:

3M™ Weatherstrip Adhesive

It even comes in 3 decorator colors… Clear, Black, & Yellow …… to expand your choices. :wink:

And if you want your nubbin to never ever come loose, use a dab of this:

3M 5200

Bottom line… just about anything will work.

BUT…. whatever you use, clean the old glue completely off both the nubbin & the rubber switch cover. This is important if you want the new glue to bond correctly.

Aquarium silicone is about as good as you’ll get for any mastic type stuff.

there is no need to disassemble the tailcap...

if a repair will be necessary on day its good to know upfront to look at a small part not to disappear.

otherwise :leave it as it is and stay happy ;)