My ETX90EC is used only with the standard hand controller. Lately it was having a problem with the RA tracking. When it was turned on the telescope made the normal startup movement in declination but the RA tracking did not start. It took several on-off tries to eventually get the RA tracking to catch. At this point I decided to check what was going on. The telescope and mount were placed in a small table over a towel. The mount bottom plate was removed. This is easy. There are three flat head screws covered by the small round rubber pads. As soon as these are removed the bottom plate comes out easily. Remove the batteries first!. Everything looked normal in there so I started to push carefully on all connectors and found that there was one almost about to fall off. This connector apparently applies voltage to the motor that runs the encoder. The looseness was causing an intermittent contact. I also cleaned the encoder just in case. There was some grease nearby and about to creep in. A test indicated that this contact was the most probable culprit.
The photos show first the bottom of the ETX90EC fork mount with plate removed and second a close up view (a bit defocused) with the arrow pointing to the loose connector. Just in case someone else has been dealing with this problem too.