Meade ETX-90 with computerized mount slews too far during auto-alignment I've been trying to get my new ETX-90 to properly align itself these past few nights, but without success.  I've mostly been using the Easy align functionality, which has been choosing Arcturus and Altair as target stars.  Arcturus can become obscured by trees later in the night from my viewing location, but I can see it early enough in the night to use it for aligning the telescope.

The problem, as the title suggests, is that when the telescope starts the alignment process, it slews right past Arcturus (and to a lesser extent, above it).  The same thing happens if I do manage to get a fix on Arcturus and continue on to Altair.  If I try, instead, to perform a two star alignment, choosing Altair as the first star, the telescope will slew over 180°.  In both cases, after fixing on both stars Autostar complains that I didn't perform the alignment correctly.

It seems like the gear ratios are incorrect, however I've verified that they are the factory defaults, and have even performed a reset.  I've also tried to calibrate the motors and train the drives, using a landmark about 100m from my viewing location, although I don't own an eyepiece with a reticle.  The time is correct, and the location should be close enough (within a few arc-minutes), so nothing else seems wrong with my setup.

This doesn't seem like a common problem, since none of my other research has turned up similar situations.  My most reasonable guess is that the gear ratios are in fact wrong, which would lead me to believe my new telescope is in fact not new, and has non-standard gears.  I haven't opened it up to verify that, though.

Is there a more plausible explanation and solution to my problem?
It seems unlikely that it would have non standard gears.  On the ETX forum that Bonnie refers to there is a thread about a problem similar to yours - its one of the earliest posts.  The problem turned out be grease on an encoder, which when cleaned off, fixed the problem.