Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail
From: Frank Krygowski <frkrygow@sbcglobal.net>
Newsgroups: rec.bicycles.tech
Subject: For those who believe in electricity
Date: Sun, 6 Apr 2025 22:22:33 -0400
Organization: A noiseless patient Spider
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I'm not an electronics guy. But speaking of problems, I think I 
mentioned a few days ago that on a recent night ride, my headlight (B&M 
Eyc N plus),  powered by my good old sidewall generator, was randomly 
and sporadically blinking off. I put the bike on the workstand, checked 
out the wiring (it’s original and pristine), and spent some time 
spinning the front wheel. Sometimes the headlight worked, sometimes not, 
and it changed state at random without having been touched. I was 
suspicious of the tiny on/off switch hidden behind a rubber plug, in 
part because I felt no satisfying click.

I substituted a different (lower quality) LED dynamo light, which seemed 
to work perfectly and probably absolved the generator. I eventually 
talked by phone to Peter White, who sold me the light far longer ago 
than I remembered - ten years! I asked if he had clues on diagnosing the 
problem. He did not, but suggested that the identical light without the 
possible failure point of an  on/off switch is just $35. (A sidewall 
dyno doesn't need a switch.) Still, I opted to open the light to see if 
I could spot anything because I have a compulsion about fixing things - 
but a headlight has to be really, really reliable.

Here are photos of the electronic guts, with a vernier caliper for size 
(and to educate Tom!).

Bottom view. The downward facing LED is at the top of the photo, the 
suspicious switch is the tiny white box at the photo’s bottom. 
https://www.flickr.com/photos/16972296@N08/54435279894/in/dateposted-public/

Top of the circuit board. The large copper pad is part of the heat sink 
system, contacting a metal casting that forms the top of the headlamp 
body. I’ll probably add some heat conducting goop when I reassemble:
https://www.flickr.com/photos/16972296@N08/54435279589/in/dateposted-public/

Although a bike generator or dynamo puts out AC, I had hoped to diagnose 
it using DC, figuring a 6 volt battery would essentially supply half of 
the sine wave so half of the input circuit. That naturally works with 
incandescents, and it worked with one Avenir LED dyno headlight that I 
repaired. Not so in this case. So I ran another generator using a roller 
chucked in my drill press, attached a digital voltmeter in parallel, and 
poked around best I could. I saw nothing loose, no scorched components, 
nothing obviously wrong.

With no power attached, I tried checking for continuity across the 
switch. It always showed close to zero ohms, never infinity - but the 
resistance readings with pinpoint probes were jumpy, and since the 
switch wasn’t isolated from the circuit, that may not mean much.

I used contact cleaner to blast out the switch and repeatedly clicked 
it, including while power was applied. Except for a few occasions, the 
light did not respond to the switch, so I still suspect the switch. When 
the light was off, I had about 12 VDC. When on, about 4 VDC.

It’s still not fixed, but it's getting late here. I would try to simply 
short out the switch, but it’s very difficult to identify and reach its 
microscopic solder pads and I’m no good at micro soldering.  I think my 
best bet will be to mechanically remove the switch, crushing and cutting 
it as necessary, hoping that it will yield access to solder points that 
I can bridge with a short. If that cures it, fine. And I’ll probably buy 
that other light anyway.

BTW, Peter White is not pleased about the tariff situation. He says he 
won’t raise prices on current stock, but with the next shipment he’ll 
probably have to.

-- 
- Frank Krygowski