In our decoder installation work we have now experienced several instances of motor shorts in theAthearn Ready-To-Run (RTR) series of locomotives. The short is caused by the bottom motor brush clip grounding to the frame. This does not pose a problem in DC operation, only after a DCC decoder is installed.
The RTR mechanism is basically the same as the old “Blue Box” design. For older Blue Box Series, some of us remember removing the motor to isolate that bottom clip from the frame when installing a decoder. That is what is supposed to be done on the RTR series, however, too much solder on the bottom clip and/or over-tightening of the motor mounting screws are two circumstances that can lead to the problem.
Unfortunately, there is no reliable way to test for this and the condition may be constant or intermittent. In some instances it could fry the decoder.
If you are purchasing an Athearn RTR loco for sound or decoder installation, and you are performing the installation yourself, please be guided by the above.