Let's not forget there have been runs with defective crimps at the terminals. I have seen engine harness to drawbar defective and with too much strain. Defective solder on drawbar pins, and also defective in ability to carry current. Good continuity but not under load. Bad connector on tender harness, both plastic connector not holding terminal in (pushes out) and the bad crimp mentioned earlier.
Some of these later runs have had defective wiring and molex plugs too. That run of N&W J required several fixes to get sounds, and motion right.
I have to agree with John, loss of 5V, PCB ground (definitely), or Data (probably) I would have thought would also have led to other issues beside a periodic chuff miss. Like lights flicker, smoke off. G
