My Celestron mount slews in the wrong direction. Is this an encoder problem?

It could be an encoder problem. The encoder is a light-emitting diode (LED) device that measures how much the motor has turned. Try this general test of the encoders:

For Alt-Azimuth mounts: select Utilities-Get Alt-AZ. For CGE mounts: select Utilities > Get Axis Position.
The LCD display will show lines for azimuth and altitude in degrees-minutes-seconds format. Select a slow rate by pressing Rate 2. Now use the arrow-direction buttons:

Up arrow - altitude increases sequentially
Down arrow - altitude decreases sequentially
Right Arrow - azimuth increases sequentially
Left Arrow - azimuth decreases sequentially

If the numbers go the wrong way, there is a problem. (Be sure to check Scope Setup – Direction Buttons as well if they are moving the wrong way to eliminate this setting as the problem.)

At rate 2, the scope moves at the same rate as the sky–15 seconds of arc per second of time. The numbers in the hand control display refresh about 1-2 times per second. The seconds numbers should change between 5 and 15 between display refreshes. If it is much less or much more than this, there is a problem.

Contact Celestron for factory service and parts to fix your scope.