>Can it loose polarity during use? Charging was ok. when I took my Beam to
>the traffic about 6 weeks ago, and it vanished about 3 weeks ago?
Not very likely.
>I tried to connect field windings straight from the battery during run, but
>I could see no effect (well, I did not see the ammeter either!)
This sounds like the current cutout, or the voltage cut in contacts are defective.
Bert Clewits tells there being 2 coil and 3 coil regulators. The 2 coil regulators integrate the cutout and the cut in contacts on the same relay.
Since a seemingly saturated field coild produces no charge, here are some tests,
1) Remove the field wire from the dynamo, and measure the field resistance to ground. Should be very low (less than 2 ohms). Do this at the wire at the regulator (pin F). This clears the field and field wire of wrongdoing.
2) With field wire connected to the battery, measure the voltage on the dynamo output terminal. It should be about 13v at 1100 RPM, and higher at higher RPMs. With open contacts, it could go as high as 25 volts. Do this at the wire at the regulator (pin D). This clears the dynamo of wrongdoing.
3) Does the regulator have a good ground (pin E)? Regulator ground is good.
4) Do both pins A and A1 show ~+13.5v "battery voltage"? This clears the solenoid to regulator wiring and ammeter "if fitted".
With all wires re-connected and the key switched to on "engine off", you should measure...
1) Battery voltage at "Pin F", if not, then the regulators field relay is bad, or mal-adjusted.
2) Low voltage at "Pin D" perhaps less than a volt. This is because the charging lamp returns through "pin D" into the regulator relays and the generator windings.
When all is well and working, the field coil will vibrate as is modulates the field current while regulating the voltage. The voltage cut in relay wil visibly move somewhere above 1000 RPM. The current cut out relay will open at around 30 amps "good luck verifiying this".
The Lucas regulators(3 coil) are easily adjusted, but the japanese aftermarket ones (2 coil) require bending terminals to adjust anything, which is dificult/touchy and it is very easy to short stuff out in the regulator.
I hope this helps a bit, and let us know.
Jarrid Gross