ETX TECHNICAL TIPS Last updated: 15 November 2002

ETX-105 DEC drive "jitters"

Sent:	Wednesday, November 13, 2002 6:50:46
From:	dcrocker@mwdh2o.com (Crocker,David J)
After much research and reading of your great site, I purchased an
ETX-105. The Scope is all I hoped it would be, however the DEC drive had
'jitters'. It looked like the scope had a heartbeat as it tracked an
object and the image jumped both up and down in the eyepiece as it
slewed.  The RA drive was glassy smooth so I knew there was a problem
with the DEC drive.  Reading all of the fixes for the other ETX's on
your site I decided to open it up and see if I could smooth it out. 
It's not the same!  However,  it's not hard to get at the drive without
removing the OTA.  There are two screws on the inside of the right arm
(from the eyepiece holder end) and one screw on the outside of the arm
at the top ( remove the locking knob and circle to see this one). 
Remove these screws and the outside cover will be free to swing down and
off.  The big difference once you're inside is that the worm gear frame
has two allen head 'jacking' screws that force the worm gear into the
ring gear.  These screws were way to tight, forcing the worm gear to
bind on the ring gear.  I loosened the three philips head screws that
hold the worm gear frame to the arm and then loosened the jacking screws
as I watched the drive operate.  When I could see the gear action smooth
out I retightened the philips head screws.  I gave the whole motor/gear
assembly a light tug and found that it was very loose (1/4 inch of play)
so I tightened the two screws on the gear box just until the movement
was gone.  After reassembly of the arm cover I found that nearly all of
the jitters are gone. I reset the autostar, retrained the drives and am
now very happy with my new scope.  I hope this helps others.

-Dave Crocker

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