If you have no luck by now, you are most likely to have a failed alternator stator.
If the engine is due to come out anyway - change the stator.
Remove the screws which secure the stator to the bracket and the complete motor and head assembly will lift off the bracket.
Still no luck, turn the stator the other way.
Whilst diagnosis is simple, replacing a stator does mean removal of the engine and rear crankcase cover.