John, thank you for the idea. I took a second loco and a powered car (smoking reefer) off the layout and powered up the layout - rear coupler will still not fire. Per John's suggestion, I put a finger on the rear coupler while firing it with the Universal remote, and I could feel a faint vibration. I did the same for the front coupler, and there was a noticably stronger vibration. So it seems there's at least some power getting to the rear coupler. Do I have any more options before calling a service center? Thanks again for all the help!