ETX TECHNICAL TIPS Last updated: 6 December 2004

ETX-90RA drive fix

Sent:	Monday, December 6, 2004 11:47:28
From:	Harden Schaeffer (aitchbar@yahoo.com)
I've seen quite a few complaints about the slow pickup of the drive on
the ETX-90RA.  I found a cure for that and also for "jumping" (the drive
will stop for several seconds, then jump ahead to where it's supposed to
be).  After sending the scope back to Meade twice for these problems
(under warranty) and not getting any help I decided to do something
myself.

First, I called Meade and found out that the grease they use is
Molybdenum grease, so I went out and bought a stick.  Then the procedure
is:

1.   Release RA lock fully, then remove battery cover as if you were
going to change batteries.

2.   There is a one-quarter inch hex-head screw in the center of the
drive base, accessible through a notch in the circuit board.  Loosen
this fully, and remove the base.

3.   There is a bracket that holds the large drive gear in place. 
Remove the 3 Phillips-head screws holding it and remove the bracket.

4.   Lift the gear off the hub.  I'm talking about the gear that is
about 4 1/4 inches in diameter with about a 2 inch hub.

5.   The problem is this big gear is quite loose on its hub.  We need to
shim the hub so the gear still rotates freely, but doesn't have a lot of
lateral play.  If you can get some shim stock of the right thickness cut
a piece the width of the hub and the right length so it ALMOST
completely circles the hub. There's no shim stock available in my town,
so I made a shim by folding some oven-grade aluminum foil over a couple
of times.  Just be sure the gear still turns freely on the hub.

6.   Grease the livin' heck out of the gear center, hub, and shim.  I
really laid the moly grease on thick.

7.   Put it all back together, being careful that the gear retaining
bracket goes in the groove in the gear. It will try to get on top of the
gear if it can.

8.   Reassemble the telescope and enjoy the smooth, quick pick-up of the
drive.

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