Quick update -
I ordered the new MOSFETs. They should arrive next week.
I removed both MOSFETs from each channel (C&D) for a total of four from the main control board. One MOSFET on each channel was bad (the lower position). I ran my multi-meter on the empty pads/spots where they were mounted. All typical response except on the lower MOSFET position (Q11) on channel D. I get 300 ohms across the gate (top tab position of the MOSFET) and source (bottom tab position of the MOSFET). The center tab position (drain) was open and appears normal when compared to other readings. When I attempted to follow the traces from the Q11 position, I think there is a surface mounted chip that is damaged in the DP12 position shown on the attached photo. No idea what it is. My guess is that this will render channel D non-usable.
Maybe I will look for a spare "bad" board (Lionel P/N 691ZWPC100) that I can salvage parts (chips) from.
Any thoughts?
