John,
Thanks for the note. Understood. I was covering the basis.
If he did hear a chuff sound, I would be tempted to say the engine communications board (R2LC) is most likely also OK. But I would test other functions as well, including changes in the tender lighting (reverse), the sound of the rear coupler opening, etc.
I suspect it's the motor control board, just need to verify a couple of things before I would recommend he purchase a $100.00 (plus shipping) replacement board.