It's time to get further into the weeds. As John mentioned above, I'd start with giving the motor a good once-over to verify all is well there. Once that's done, move onto the wiring and electronics.
Based upon your description, the ACDR motor driver is suspect, but it's important to go over the motor to be certain nothing there caused the ACDR to fail in the first place. Or it might be something else... we're kind of at the limits of what can be diagnosed remotely.
If you're uncomfortable with going further, I can have a look at your locomotive, or I'm sure John or others on the forum can do the same.