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I needed to clarify the wire connections in the electrical drawing (schematic), that is to say where an electrical connection occurs as indicated by the black dot at the intersection of a three-wire junction.

If there is no black dot where two wires cross over each other there is no connection between the wires.

The larger power diodes are pressed into an integral heat sink. The problem with a faulty power diode would be sourcing a replacement since they haven't been available for decades. Another power diode could be substituted for a bad diode, but it would need to have substantial surface contact with the heat sink in the regulator's case for thermal conductivity (cooling).

Thanks Jim.
It's very helpful that you included the note (at the top left corner) in the drawing itself, rather than just in a separate message.
Helps to figure out what was going on.