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From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: Re: For those who believe in electricity
Date: Wed, 9 Apr 2025 12:13:00 -0400
Organization: A noiseless patient Spider
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On 4/8/2025 8:56 PM, Frank Krygowski wrote:
>  
> The switch is the tiny white box toward the bottom of this photo:
> https://www.flickr.com/photos/16972296@N08/54435279894/in/dateposted- 
> public/ just below "3R 46 16V" which is probably a capacitor. The black 
> pushbutton sticks out downward in the photo (or backwards, in the 
> mounted headlight) and looks odd in the photo, again because of 
> reflections. That switch is about 4.5mm x 2.5mm x 1.8mm tall. I removed 
> the switch from the circuit board.
> 
> I had assumed it was a toggle, but it seems instead to be a momentary 
> switch. It connects to five tiny solder pads. The two big ones, at the 
> "bottom" of the switch in the photo, are just for fastening it to the 
> board. At the "top" face in the photo are three very tiny pads, call 
> them A, B and C.
> 
> Playing with a jumper wire ending in two sharp pins, I found that 
> momentary contact from A to C changed the state of the light, on to off 
> to back on, etc. A to B did the same. I had to be careful to touch 
> fairly quickly and not bounce.
> 
> At last check, the light is in "on" state. I think if I don't disturb 
> things, it should stay in that state, and I can try reassembling and 
> testing it on the bike. I've got other stuff to work on tonight, so I'll 
> get back to it tomorrow.

More bench testing this morning. The headlamp started right up, 
perfectly consistently when driven by the dynamo spun with my drill 
press. Momentarily jumping A to C (or B) of those switch solder pads 
toggled the lamp on or off while running the dynamo. Shutting down the 
dynamo put the lamp into "standlight" mode. In that mode, with no 
voltage input, jumping A to C turned off the standlight. Applying power 
turned the lamp back on, no switching necessary. It seems the headlight 
is operating as it should.

I'm convinced the problem was that faulty switch, probably with internal 
parts rattling around enough to occasionally toggle that A to C or A to 
B contact. I suspect it will work fine if I successfully reassemble it 
without the switch.

It's still slightly worrisome, because a headlight really does have to 
be reliable. Maybe I'll carry a little battery light as a spare for a 
while. I often do that anyway when night riding with others, because of 
so many incidents of other folks' headlights failing on rides.

-- 
- Frank Krygowski