Fast Forward Only - Only Loco -Help please...

Sure sounds like the Odyssey is failing to see the tach pulses.

One of the features I liked about the TAS EOB unit was they had a little LED on the encoder board that you could visually verify that the encoder was seeing the flywheel tach tape.  The Lionel Odyssey you just have to take it on faith.

The next step is probably parts replacement unless you have an oscilloscope and know how to use it.  My next step would be to see if pulses are coming from the encoder.

If that locomotive has a Odyssey switch, try turning it off.  The older ones often didn't have a switch to disable it.

Well, I have the parts for TMCC locomotives, so when I have an issue, I just dig them out and start swapping.  I agree that if you don't have spare parts, swapping parts gets expensive in a hurry!

Top suspect here is either wiring to the motors and sensor or the motor driver board.  It could be the R2LC, but that would be down my list of suspects in this case.

You can have several problems that cause this, R2LC, Motor Driver, the encoder that you replaced or the four wire PMW connector. One suggestion is to replace the Motor Driver with the ERR Cruise Commander "M" odyssey diesel. That would eliminate the encoder and motor driver. At this point, I believe the best solution would be to take it to your local repair center.

Bill

I wouldn't rush off to an unknown repair place, you could end up worse off than you are, and poorer as well!

If you were near SE-PA, I'd fix it for you.  As Bill said, one upgrade would be the ERR Cruise Commander M, it usually does a better job than Odyssey I from Lionel.  I've had mixed results with the first version of Odyssey, the Legacy Odyssey II is great.