I have a 1975 850 T3 which I have owned for 25 +years. I thought I knew my way round it pretty well but have encountered a charging problem which I can't seem to sort out. Here is what I have checked so far:
Note I am using a decent meter (one of those one with a reference cell in it)...
Battery is good and holds it's charge.
Charge light is working correctly when used with the Bosch rectifier but is staying on when revs are increased.
resistance across slip rings seems to be correct (used the value in the Haynes manual) definitely not infinite!
Resistance across the 3 yellow wires seems to be approx correct as in Haynes manual
I know that one of the diodes on my rectifier went a few years ago (20!!) and I replaced it and the thing seems to have worked reasonably well since then.
This time round I Initially tried replacing the rectifier with a used Newtronics unit bought off e bay. No difference with this except that the idiot light does not function but in both cases (Bosch and Newtronics) I can only detect a very small AC output across the yellow wires when the engine is running..
Both the Newtronics and the original Bosch unit give the same symptoms ie that I cannot measure 12 volts across the slip rings when the ignition is switched on and then engine is stationary and also that I can only measure a very small AC voltage with the engine running.
Surely I should be able to detect 12 v DC at the terminal where the brush is labelled DF (brown wire) and also at the blue stator connection before the thing will start to produce 12-14V AC across the yellow wires.
I have checked the red current carrying wire from the ignition switch and can measure 12 v at the input to the voltage regulator with the ignition on and obviously also at the rectifier.
So...why is there no 12v at the alternator (+) brush terminal (brown wire)...is this a regulator fault? How can I test it?
Any help gratefully appreciated.
Note I am using a decent meter (one of those one with a reference cell in it)...
Battery is good and holds it's charge.
Charge light is working correctly when used with the Bosch rectifier but is staying on when revs are increased.
resistance across slip rings seems to be correct (used the value in the Haynes manual) definitely not infinite!
Resistance across the 3 yellow wires seems to be approx correct as in Haynes manual
I know that one of the diodes on my rectifier went a few years ago (20!!) and I replaced it and the thing seems to have worked reasonably well since then.
This time round I Initially tried replacing the rectifier with a used Newtronics unit bought off e bay. No difference with this except that the idiot light does not function but in both cases (Bosch and Newtronics) I can only detect a very small AC output across the yellow wires when the engine is running..
Both the Newtronics and the original Bosch unit give the same symptoms ie that I cannot measure 12 volts across the slip rings when the ignition is switched on and then engine is stationary and also that I can only measure a very small AC voltage with the engine running.
Surely I should be able to detect 12 v DC at the terminal where the brush is labelled DF (brown wire) and also at the blue stator connection before the thing will start to produce 12-14V AC across the yellow wires.
I have checked the red current carrying wire from the ignition switch and can measure 12 v at the input to the voltage regulator with the ignition on and obviously also at the rectifier.
So...why is there no 12v at the alternator (+) brush terminal (brown wire)...is this a regulator fault? How can I test it?
Any help gratefully appreciated.