That glowering red eye!

Staring at me from the dash of the 100Gs.

I did the quick test from the BMW manual: jumper wire across the blue and black leads to the regulator and it's the alternator at fault apparently. I assume I now have to check the stator and rotor separately. Can these be checked in situ (after disconnecting the battery) or do I have to remove them?

Does it stay on all the time at the same intensity OR does the intensity change when you are on the move ....... i.e. it gets dimer and then brighter

If I remember Rob Farmer is very good on Airhead electrics

if the light stays on all the time, (at the same intensity), check the following before you start talking the diode board and rotor off

the wire from diode board to voltage regulator and make sure that it is OK

not looked at one for some time - but I remember having a problem with a break in that wire

Have you still got the original OEM diode board fitted, (the BM one is dodgy and can overheat), - I always used to change mine to ???? forget the name

remembered the name Thunderchild - replacement diode boards

Bright red all the time! So suspect either rotor or one or more of the windings are fecked.

Quick and easy check for the rotor.
Front cover off, lift brushes off rotor and check the resistance across the two rotor slip rings, should read 5.6ish

I seem to remember that if the gen light comes on the rotor is probably good

If the gen light stay on solid then it is diode board or wiring

If gen light gets dim can be diode, wiring or bad earth

It is worthwhile doing the obvious checks - i.e. battery earth, looking at wiring, before removing the diode board and rotor

Neil - should he also check the voltage across the bushes - at idle and when revved

I have a spare diode board if you want to borrow.

Now this is why people join here; friendly and helpful advice.

God bless all of you.

Tractors are go said:

Now this is why people join here; friendly and helpful advice.

God bless all of you.

Click to expand...

Aye, not such a bad bunch.

Thanks for the advice / offers gents. Time to get busy with the multimeter methinks!

All on Utube these days

this may help in testing the Rotor

https://www.youtube.com/watch?v=oxQwx5EC5X4

note the different resistance reading between series

Ta. I had a look at youtube. I also whipped off the stator and tested the three phases 0.8 ohms in each case. Manual says below 1 ohm is fine. Hmmmmm ... Then each phase to earth (the casing anyway) and got an open circuit. Hmmmmm ...

Checked the rotor. Got 3.6 ohms across the slip rings. Open circuit between each ring and earth. Hmmmm ...

Beginning to look a lot like the diode board!

scotboxer said:

Ta. I had a look at youtube. I also whipped off the stator and tested the three phases 0.8 ohms in each case. Manual says below 1 ohm is fine. Hmmmmm ... Then each phase to earth (the casing anyway) and got an open circuit. Hmmmmm ...

Checked the rotor. Got 3.6 ohms across the slip rings. Open circuit between each ring and earth. Hmmmm ...

Beginning to look a lot like the diode board!

Click to expand...

Good luck - let us know when you sort it

Diode Boards - I think the problem with OEM ones are that they overheat as I think, (it's a long time ago) they are some kind of heat sink

as I said bought a few Thunderchild ones from the US and replace mine - Rick from Motosomething, (??) sells them and there is a good article somewhere on the web that he wrote

I've just been through a similar exercise....

http://www.ukgser.com/forums/showthread.php/456223-R80-charging-problem

After replacing the rotor and regulator I've now fitted a new rectifier after trying a secondhand one which cured the problem.... more or less as there was still an intermittent glowing of the Gen light.

I've now fitted the new rectifier with an additional earthing lead from one of the ground mounting bolts on the casing (top left looking at it from the front). I've a suspicion that when I did the rebuild all the newly painted casings may have stopped me getting a good ground for the rectifier.

After all the expense I almost wish I'd gone for a new combined rectifier/regulator/heat sink! The rotor was out of spec.

I've got a working regulator if you need one.

So ... update. Pulled the diode board and checked the 6 main diodes. All seem to be OK. i.e. they pass current in one direction only when I test for resistance across the 3 connectors to earth and ditto when directly on the solder at the front of the board. Well, they do for a second or so and then revert to open circuit. Is this a peculiarity of a diode? Sheesh ... the plot thickens.

scotboxer said:

So ... update. Pulled the diode board and checked the 6 main diodes. All seem to be OK. i.e. they pass current in one direction only when I test for resistance across the 3 connectors to earth and ditto when directly on the solder at the front of the board. Well, they do for a second or so and then revert to open circuit. Is this a peculiarity of a diode? Sheesh ... the plot thickens.

Click to expand...

Rob Frankham - published an article on "Testing the Diode Board"

I am not sure where I got it from - but it was in the Public Domain - (probably the BMW Club site) - anyway here it is - CREDIT TO ROB FRANKHAM - hope it helps

here it is

Testing the Diode Board
Description
The diode board is basically an assemblage of 11 separate diodes connected together in one package. The main function of the board is to rectify the alternating current produced by the alternator and turn it into direct current that can be used to charge the battery and run the rest of the bikes electrical system. It also has a secondary function, which is to supply, via a separate set of three diodes, the field coil that provides the magnetic field, which is used to generate the output from the alternator. In order to do this, the diodes are arranged as shown below.
Each Diode is a 'non return valve' for electricity and so should pass current in one direction but not the other .In order to test the diodes, you need some form of continuity tester. This can either be a bought tester or a perfectly satisfactory alternative can be made using a battery, a bulb, a couple of crocodile clips and a few bits of wire arranged as shown below.
First remove all connections from the Diode Board. It is actually easier if you remove the board from the bike. Now, referring to the diagram below:-
Connections:
1. B+ Positive line to battery - Thick Red or Black wire (T)
2. Not normally used
3. Thick Wire from alternator to diode board (1 of 3) (U)
4. Thick Wire from alternator to diode board (1 of 3) (V)
5. Thick Wire from alternator to diode board (1 of 3) (W)
6. Wire from D+ on voltage regulator (S)
7. Thin Wire from alternator to diode board (Y)
Procedure
1) Connect the negative clip (marked -) on the continuity tester to terminal number 1 then connect the Positive clip (marked +) to each of terminals 3,4 & 5 in turn. In each case, the bulb should light (or the continuity tester should indicate a circuit).
2) Swop the clips so that the positive clip is attached to terminal 1 and the negative terminal connects to 3,4 & 5 in turn. Now the bulb should NOT light. (The Continuity tester should not indicate a circuit).
3) If you examine terminals 1 & 2 you should find that they are firmly fixed to one of the two metal frames of the diode board. Got to the other metal frame and attach the positive clip to it. Now again attach the negative clip to each of terminals 3,4 & 5 in turn. In each case the bulb should light (I'm going to ignore the bit about the continuity tester from now on, I'm sure you get the picture!)
4) Now attach the Negative clip to the same metal frame and attach the positive clip to terminals 3,4 & 5 in turn. Now the bulb should NOT light.
The preceding four stages test the main rectifier diodes. If the results are not as shown, this indicates that one of these diodes is dead. There's no point in going any further, it's not practical to replace them so you might just as well bite the bullet and order a new diode board. If you've got this far without hitting the problem, then move on to the field diodes.
5) Attach the negative clip to terminal 6 on the diagram and once again connect the positive clip to terminals 3,4 & 5 in turn. The bulb should light.
6) Now put the positive clip onto terminal 6 and the negative clip to 3,4 & 5 in turn. The bulb should NOT light.
That deals with the three field diodes. This just leaves the last two diodes which connect the centre of the 'star wound' alternator into the circuit.
7) Finally connect the positive clip to terminal 7 and the negative to terminal 1. The bulb should light. Now move the negative clip to the same metal frame as mentioned above. The bulb should not light.
8) connect the negative clip to terminal 7 and the positive clip to terminal 1. The bulb should not light. Move the positive clip to the metal frame and the bulb should light.
This completes the diode tests.
It is possible to replace one of the small diodes if you're handy with a soldering iron, and it is certainly a lot cheaper than replacing the diode board. I'd suggest a diode rated at least 4 amps at 100 volts for the job. I have done this. It lasted for at least 20,000 miles and was still going strong when I got rid of the bike. The only thing you have to do is make sure that you put it in the right way round.
R. Frankham

Well its time! Had you been near my lock up last night, you would have seen a blue haze around it! Not exhaust smoke. Just me swearing ... at myself. I omitted to mention that I had taken the starter out for a quick clean and lube of the pinion. Steppers and Jay would likely have worked it out from that clue! Guess which complete numpty managed to forget to connect the lead from the starter to the diode board. It had fallen below the starter and got jammed there and I missed it when replacing same. Feck! Feckity feck feck feck! Mea maxima culpa! At least I got a master class in old Boxer charging systems!

Anyway. Now sorted and the fierce red glow is now a mere glimmer. Checked the voltage across the battery when the bike was running at 1.5 - 2k and got 11.5 V. Used a fat copper jump lead to short circuit the earth pole to one of the engine mounts: no difference. So, Houston, we still have a problem! My plan is to check the output from the generator and replace the brushes anyway. A new voltage regulator is on the cards although I'd have expected that to be fried and U/S rather than putting out inadequate charge. All that is going to have to wait as I am off to Germany next week and I have a room to paint when I get back.