FW3A Troubleshooting / FAQ

Best to just leave the tailcap alone, don’t take it off. Insert the battery from the head.
There’s a warning in the box, stating this.

Use Plastic Super glue. Your local hardware store probably has it.

The package comes with the tube of glue and a pen. You wipe the pen over both surfaces to be glued, wait 1 minute, then apply the glue.

It makes super glue stick extremely well to rubber.

Thanks, never knew about this type. Good to know.

After a few hundred cycles, it seems my bottle cap’s plastic is too soft. It’s flattened out. I need some harder plastic.

Maybe try epoxy putty from your local hardware store or hobby shop.

The advantage of epoxy putty is you can easily shape it to exactly the shape you want. And it cures hard.

delusional wrote:
What’s a nubbin? It’s not much.
It’s a little cylinder of plastic, shown on the left here:

Picture credit to JasonWW

The nubbin fits into the center ring of the larger piece of rubber, and they both go into the FW3A’s switch mechanism.
The Switch of an FW3A will not work without the nubbin.

When you twist off the tailcap of an FW3A, the switch mechanism falls apart.
They were saying something about glueing the switch, but it didn’t happen, might happen in the future, who knows?
In the meantime, the nubbin is very easy to lose. I opened my tailcap once with no problem, but on the second time I lost my nubbin.
I didn’t even know there was “nubbin to lose.” So I wasn’t really watching for it. Now I need a new nubbin.


It took me about three minutes to make a new nubbin.
I took out one security bit, marked CR-V4, from a set.
You can see it’s got an outer rim and a cup in the middle. This is designed for “security” screws.


Next I hammered the bit through a plastic drink bottle cap. See the left hole? This did not work because my nubbin got stuck inside the cup of the bit. I damaged the nubbin prying it out.
On the second attempt I stopped a little short, leaving a bit of plastic remaining around the outer ring, and the nubbin was still attached to the cap. I cut the nubbin from the cap with a knife.
See the nubbin on the right, still attached?


And finally, you can see my new nubbin, in it’s new home, ready to reinstall in my FW3A.
It seems to work really well. …. at least it’s been holding up very well for a few hours.
You also see the drill bit on top, and on the left, the nubbin that got damaged.

I had a half dozen more bad puns ready to go, but decided it’s better if I don’t.
If others would like to join in, there’s nubbin stopping you.

@ delusional … If you want to resize your pics I’ll delete this. :wink:

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.