I have been trying to fix an ETX90-EC. Each time I fix a problem new one appears. The latest one is from RA drive gear train. The gears appear to be OK because I do not see any broken teeth on any gear. When I press the East or West button the motor runs for a while and then suddenly the noise gets louder and drive movement stops. I see the 1st gear vibrating while spinning and apparently slipping from the next gear. The clamps are all tight and I have tried pressing them down with my fingers. No teeth are broken on any gear. This has been extremely frustrating so far..