Most older locomotives will require a hard wired decoder, and probably some major frame modifications to become DCC compatible. Typically, the motor needs to be isolated from the frame.
This particular locomotive has a DC circuit board that is apparently faulty, but the locomotive seems like it would run fine, and since I am going to DCC, I thought this one might be a likely candidate. With the dc circuit board up and out of the way, motor runs and everything goes round and round when I apply juice to the motor and to the frame. Doesn't that mean that the motor is isolated from the frame?
not necessarily. Since you say "motor runs...when I apply... to motor and to frame", then the motor is connected to the frame. The board was probably for lights. If the motor is ISOLATED from the frame, then it is DCC compatible. Not difficult to isolate in most case, just a step that needs to be done. Otherwise, the first power to the loco lets all the magic smoke out of the decoder.
During the night I thought about what I said and it occurred to me just what you said, that if one leg of juice goes to the frame, the motor must not be isolated? Thanks