Re: For those who believe in electricity

On Sun, 6 Apr 2025 22:22:33 -0400, Frank Krygowski
<frkrygow@sbcglobal.net> wrote:

I have a some time right now.  I'll try to answer Frank's original
question and avoid the inevitable topic drift.  Please forgive my
being rather terse.

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.

It the light this one?
<https://www.rivbike.com/products/b-m-eyc-t-senso-plus-dyno-headlight>
I couldn't find a "good old sidewall generator".  Could you be a bit
more specific?

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.

Start by isolating the problem.  Is the intermittent light in the
generator (dynamo) section or in the light?  Find a different dynamo
to power the light or move the light to a different bicycles with a
different power source.  If replacing the dynamo magically fixes the
problem, I suggest that you tear the dynamo apart and clean it out.

Next, pull on the wires between the dynamo and light.  Yes, I said
PULL.  If the copper wire falls apart and the insulating jacket
stretches and narrows at the beak point, you've found the problem.  If
the light refuses to work after you've pulled on the wires, you
probably have a broken wire somewhere that's hiding under the
insulation.

If it's not in the dynamo or the wiring, then it must be in the light.
Start with an electric tooth brush.  The idea is to use it as a
vibrator to isolate the section that has gone intermittent.  If the
vibrating tooth brush doesn't crack your teeth when used in the
originally intended manner, it's probably safe to use on a bicycle
light.  The most likely areas are loose magnets, corroded switches,
corroded electrical contacts, broken PCB (printed circuit board)
traces, "cold" PCB solder connections, bad soldering, or intermittent
wire bonds inside the IC's (integrated circuits). 

https://www.flickr.com/photos/16972296@N08/54435279894/in/dateposted-public/
https://www.flickr.com/photos/16972296@N08/54435279589/in/dateposted-public/

Nice photos of the caliper.  However, the PCB is out of focus.  Flickr
reduces the resolution of the photo when upload.  I can see things
that might be a problem, but only if the photo has higher contrast,
more brightness (to improve depth of field, and of course, that it's
properly in focus.  I think you can improve your photos by using
multiple sources of illumination from diffuse sources.  The PCB photos
that I post on YouTube usually use two LED light sources from lamps
surrounding my desk.  With two sources, shadows are reduced.  With a
ring light, they're reduced even more.

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...

That's an important clue. 

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.

The voltage across the switch contacts should be zero volts when the
switch is on.  However, if B&M is doing something odd, it could be
something else.  I can't tell without a schematic.

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.

Sharpen a paper clip.  Wind it around the soldering iron tip.  You now
have a micro soldering iron.  Get some liquid or paste rosin flux (not
acid flux used in plumbing) and slop it on the solder pad before
soldering.  Use copper braid to suck up any excess solder.  Done use a
"solder sucker" on small pads and traces.
<https://www.google.com/search?q=copper%20braid%20soldering&udm=2>

--
Jeff Liebermann                 jeffl@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann      AE6KS    831-336-2558