Okay I see. The schematic is partially wrong or at least drawn in a way that is schematically wrong. The exciter coils produce AC which is apparently center tapped with the center tap connected to the blue wire that goes to the one brush and the capacitor from there. The two diodes are on the outside ends of the exciter winding and go the diodes to complete the circuit.
Most likely there are several corroded connections that are causing the problems. The spade connectors look old and crusty on the capacitor. and the green ground wire that goes to the capacitor bracket looks like it could cause problems with a loose and dirty connection there as well.
Come and go electrical issues are most often caused by dirty, corroded or loose connections. I would recommend a good physical cleaning and possible replacement of the spade connectors on the capacitor and the capacitor bracket and point of attachment to the end bell body. also cleaning the end bell body to stator contact points.
Contact cleaners are no substitution for a physical cleaning. They are a good wash down afterwords.
I run across people all the time that try to fix bad battery and power connections just by spraying them with contact cleaner. It never works for long if at all.
Physically cleaning the connection to the point of getting down to good metal works and then making sure that there is a firm physical contact between the different parts does work!
I'll start at the top and work through what I know to be true. I won't make any suppositions.
The exciter coil is an AC coil that is wound with the AC power windings. They all go into the stator and come out of the stator together.
The blue wire is a center tap. It routes from the (+) brush through the connector and into the stator windings (that explains why there are 7 wires in the connector. That seemed odd until you mentioned a center tap.) The end opposite the center tap is connected to the brush and the (+) connection at the cap. The other terminal of the cap is grounded.
Yes, the two diodes are at the ends of the yellow (exciter) winding.
As far as the connections, I did disconnect each spade terminal, spray with cleaner, connect/disconnect each connection at least 3 times with contact cleaner while wetting the connection - and then plugged everything back together. There is bright metal at the contact points at each connection. I did not tighten any of the connections as they felt pretty good to me. But to be certain I will pinch each female terminal a bit to ensure everything is making metal to metal contact. Or perhaps a light tinning of each terminal would ensure bright metal and perfect connections.
The ground terminals and the bell end connection point were all brushed and sprayed. I have a stainless steel brush and I'll re-clean those connections more aggressively. And I'll ensure the cap terminals are very tight.
It would be easy for me to say "I did that" in response to your suggestion that everything be cleaned. But the unit still doesn't produce power so obviously I didn't get it fixed! I'll have another go at it. I'll do the mechanical scrub and clean and tin of each joint. The brushes and rings are clean - each has been scrubbed and sprayed and the areas on each side of each ring is clean to ensure no voltage leaks away from the contact rings.
I have some gaskets coming for the engine so the engine is down for a couple of days. That gives me ample time to clean connections. I'll also fix the schematic to indicate that the blue wire is a center tap.
And later this weekend I'll be back with the results. I'll test with everything clean. If it works, all is well and I'll stop messing with it. If the results are bad, I'll take voltage readings at the AC outlet and the DC exciter voltage - Then I'll flash the cap and try again and I'll post the exciter voltage and AC output results. If it's just connections I'll be one happy guy!
Thanks again tcmtech A couple of years ago I was acting as one of the "Go To" guys on a helicopter forum. I enjoyed working a problem to the resolution. Now it's my turn on the other side of the table.
Mark
Thanks again