Last updated: 14 April 2009
Subject:	ETX-125 RA drive stops
Sent:	Monday, April 13, 2009 07:15:29
From:	Nohr Tillman (
I have read as much as I can on Mike's site and wanted one last opinion
from the experts. I have my ETX-125 (circa 2000-2001) apart for various
binding issues. Unintended consequences - the RA drive motor screws I
tightened up pushed into the stop ring, causing binding and further gear
pop. Fix is straighforward, but the reassembly I want to get right.

Looking at the black stop ring (in the pic) it looks like it wants to
straddle the post in the base. In other words the main "V" should be
placed around the base post to hold it in place and prevent it from
rotation. However, in this position, it would yield less than 360 fork
rotation. If installed away from the base post, the stop ring could
rotate and the fork could rotate somewhere less that 720 degrees stop to

Main question is: by design, should the black ring straddle the base
post, and not rotate freely (looks like how th part was designed) or not
straddle the base post and rotate as it is pushed by the upper fork
Thanks for your time,
Nohr Tillman
Troy, MI, USA, Earth


From:	P. Clay Sherrod (
The ring must be mounted so that the telescope will rotate 720 degrees
and then hit either of the stops before rotating further.  Its only
purpose is to keep the base wires from pulling too far along the trail
of motion.  Put the ring down in such a way that the two extended
segments will HIT the small protruding peg of aluminum that you see in
the left part of this photo, coming from the metal plate.  That is the
stop peg.

Dr. Clay
Arkansas Sky Observatories
MPC H45 - Petit Jean Mountain South
MPC H41 - Petit Jean Mountain
MPC H43 - Conway West


Yes, Thanks Dr. Clay! Instructions understood!
Now, I just have to shave down the drive screw that is pressing that
ring upward and binding up the base and fork assembly. This is the
reason I'm in there in the first place.
Nohr Tillman
Troy, MI, USA, Earth


Best of success on this....
Be sure and be very careful when reassembling; the wires going through
the central axle are very easily twisted and broken.
Dr. Clay


Thanks again. Utmost care is being taken, and some things (like the
base/battery cover) have been removed entirely until the mechanicals are
tuned up. Fortunately (or not) I've got the patience, touch and tools to
get into and out of this clean, so far anyway.

Hate to bother you, but one other thing you might help with: the loose
rear cell syndrome. I do hang my camera back there, and the cell is just
loose enough it make the camera just off-center of the view. It's not
falling out, nor is it threaded on. My version is shouldered on the
outside, pushed into the rear assembly, then through a metal ring and
the tube part swedged against that ring. Red locktite didn't set up in
the joint. I managed to wick it out though. Was gonna gently tap on the
flange to re-set the swedge. Any other luck with those?
Nohr Tillman
I suggest using Gorilla Glue and carefully follow the instructions....there is no other way to secure it. Dr. Clay

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