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.

  • $\begingroup$ This thread? $\endgroup$ – Mike G Aug 6 '19 at 16:48
  • $\begingroup$ @MikeG: yes that's it. $\endgroup$ – Dr Chuck Aug 6 '19 at 17:16
  • $\begingroup$ I left my telescope at the cottage, so I'll give this a try when I get back there in about a week. Thanks. $\endgroup$ – MBraedley Aug 7 '19 at 12:52
  • $\begingroup$ So I've got a newer model, and I can't see a way to get at the motors and encoders. Or at least the az motor. I also can't find any instructions for disassembly and repair. Any thoughts? $\endgroup$ – MBraedley Aug 15 '19 at 20:38
  • $\begingroup$ I can’t help with instructions for disassembly, but try the forum mentioned or just a general search. There’s probably a YouTube video about it. $\endgroup$ – Dr Chuck Aug 16 '19 at 17:11

Two things:

  1. Make sure your Autostar or Audiostar controller setup menu has the correct telescope model selected (the same controller is used on many different scopes & mounts).

  2. Make sure you are correctly starting at the "home" position. For a Meade ETX90 with Autostar, set up the mount with the control panel facing west. Loosen the clutch on the altitude axis, level the optical tube, then re-snug the altitude axis clutch. Release the horizontal axis clutch and rotate the scope gently in the counter-clockwise direction until it hits the stop. Then rotate it clockwise until the optical tube is pointing toward true north.

The tripod base should be level when you begin. It does not need to be precisely level (if you are unlevel by a few degrees, the computer will work this out through the alignment star positions.)

The ETX mounts are not particularly durable. Be gentle with all adjustments and don't over-tighten the axes.

  • $\begingroup$ This doesn't help me. I already went through step 1 when I posted the question (I would have thought that obvious). Step 2 isn't of much help because I already know how to home the telescope, and the model I own doesn't have an azimuth stop. $\endgroup$ – MBraedley Aug 15 '19 at 20:42

There is an ETX forum at


I own an LX200GPS. There is a known bug in the LX alignment software. Could be a bug in the ETX??


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