So this has been a great thread to follow and since we were already talking about relays my 803a is missing the relay at the far left as you can see in the pictures I posted. Would one of you that does have this relay i believe it is S14 be so kind as to take a close up photo of the writing that is on it so that I can source one for my unit. As I understand it is different from the rest of the ones there and it is responsible for the starter and field flash. I would very much appreciate it Thank you.Well, you just eliminated about a third of that circuit as being the problem. At this point leave CR5 alone since it isn't causing the "pop" of the breaker.
What you might do next is to swap the K12 relay with the one next to it (to the right not left) just to make sure that the relay itself isn't bad somehow. The relay to swap with is the one to the right of K12, NOT the one to the left. The one on the left is the starter/field flash switch and that is unique - there is only one of them in the unit.
The other five relays are identical.
The "stuff" in the back of the unit in your picture consists of the AC contactor which is the square thing that has the heavy wires on it and the voltage selection switch. That diode is not CR5. None of that "stuff" back there will be your problem -- it is all best left alone at this point since it is the high voltage section and it isn't going to work until the "pop" problem is solved.
I'm out of town right now; about 200 miles away from the schematic that I use, so I can come up with another idea or two on Monday....
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Oh and to the OP what ever happened with your CB1 breaker popping out did you track down what the problem was or did you just give up in July and have not been working on it since then?