ETX TECHNICAL TIPS Last updated: 19 September 2005

Subject:	Technical Memo to Help ETX-60AT Users Repair non-working Azimuth Clutch/Worm Gear
Sent:	Friday, September 16, 2005 18:58:06
From:	Christopher Scheer (cscheer@csc.com)
Had a problem with my ETX-60AT I purchased, worked great for a year,
then moved to Florida and stored it for a few months.  When I took it
out and set it up, the azimuth clutch did not engage no matter how hard
I tightened the adjustment lever.

Upon reviewing the following posting that I found in a link on your etx
site,
http://www.weasner.com/etx/techtips/Cooney_70AT_Guide/70atguide.htm I
found a couple discrepancies with the model I have and to 70AT
mentioned.  To wit, the worm gear transmission assembly on my 60AT was
NOT spring-loaded; in fact there were basically just two stantions risng
perpendicular from the slag metal base that acted, or at least were
supposed to act, like a tensioning bar to the worm gear assembly to
tension it to the azimuth drive gear.  These had either just worn apart
a bit or the plastic housing to the worm gear assembly had worn to the
point that they did not provide enough tension to hold the worm drive
assembly tight against the clutch gear.

I employed the following method to resolve the issue satisfactorily:

Problem:  ETX-60AT azimuth drive does not turn the scope (engage at all)

Symptom:  Drive clutch tightening lever is tightened as much as
feasible, azimuth drive is heard turning/functioning, but scope does not
revolve, in addition scope can be turned by hand no matter how tight the
clutch level is applied.

Materials:

Basic hand tools (screwdrivers, medium/small phillips head, socket set
w/ 18 mm and 3/8 inch sockets, needlenose pliers, exacto knife, etc)

approx. 4-5 feet of 4 lb. nylon fishing line  (MUST be 4# test) 
small tube of lithium grease 
sandpaper 

Steps: 

Note:  Some authors have described the plastic housing nut, (which has 4
posts on the top of it to secure the primary clutch washer nut) as an
"epoxied" non-threaded nut which needs to be sheared off the unit and
re-engineered.  This was not the case in my scope, the plastic nut was
in fact 'outside threaded' to the housing and I was carefully able to
unfreeze and remove it with an 18mm socket.  This saved a substantial
amount of "re-engineering".

Disassemble the base of the scope as instructed in the above link. 
Perform the basic maintenance (clean, sand the center slightly, then
re-lube clutch gear (teeth only). Remove excess grease from the worm
drive assembly, if evidence of plastic bits from wear or manufacturing
process is evident, then clean the entire assembly carefully with 90%
isopropyl alcohol, let dry, and re-lube LIGHTLY all moving parts only
with lithium ("white") grease.  Don't use stronger solvents to clean the
plastic gears (for obvious reasons).

Note:  Some authors have described the plastic housing nut, (which has 4
posts in it to secure the primary clutch washer nut) as an epoxied nut
which needs to be sheared off the unit and re-engineered.  This was not
the case in my scope, the plastic nut was in fact 'outside threaded' to
the housing and I was carefully able to unfreeze and remove it with an
18mm socket.  This saved a substantial amount of "re-engineering".

Remove the battery pack from the unit (unplug the entire pack from the
9V connection. Check the back and forth "play" on the azimuth worm gear
transmission assembly; you may notice (as I had) that there really was
no longer any, or at best very little, tensioning of the worm gear
assembly towards the axle in the base. It pretty much moved back and
forth freely.  If this is the case, then perform the following repair to
re-tension the worm gear assembly to the clutch gear:

1)  Cut an approx. 12 inch piece of the nylon fishing line (must be
approx. 4# single-thread nylon, which provides both the correct amount
of tensioning as well as being extremely stable to any lubricants,
solvents, or anything else including of course dew/water.)

2)  Pass the line through the battery pack housing and tie off tightly
to the battery housing.  You will be connecting the other end to the
small plastic hook on the top rear of the worm gear drive; I passed the
line from the 'long end' opening of the batter compartment through the
corner opening (for the power 9V connector lead to pass through) in
order to keep the tensioning line "out of the works" of the rest of the
assembly so-to-speak.

3) Measure a couple inches past the small plastic hook on the rear of
the worm gear assembly (this hook appeared to have been engineered to
hold the drive assembly back out of place against the third stantion
during the manufacturing process; I could find no other engineered use
for it) and cut the excess line off.  The line should be running in the
shortest path between the two points.  MAKE SURE you've already moved
the worm gear assembly to its innermost position (closest to the center
of the base).

3)  Make a small slip knot loop from the end and tighten the loop around
the small plastic hook on the top rear of the worm gear assembly.

4) Taughten the line as much as you can and tie it off with NO slack
whatsoever.  I simply used three slip knots reversed to get a good
non-slipping know.

REPEAT the above steps (1-4) a second time; this will provide enough
tension to keep the worm assembly firmly against the clutch gear BUT
also enough stretch to allow you to replace the base and re-engage the
worm gear to the clutch gear without too much difficulty.

I put a third tensioning line in as a precaution. (In case one broke)

At this point it's time to re-assemble.  Reassemble the lower base
(which holds the clutch gear) to the top of the base (worm gear
assembly) by first pulling the worm gear assembly towards the outside
rim of the housing.  You may have to experiment a few tries, but you
should be able to find the right place to stretch the tensioning
(fishing) lines to, to allow you to re-attach the clutch gear base and
then get the worm gear firmly engaging the clutch gear.  The fishing
line will not snap back immediately, so this allows a second or two to
get the bottom base re-attached to top with all gears engaged.  Once you
have the clutch base re-attached loosely to the upper base, you can use
your finger or a pair of needlenose pliers to reach into the battery
compartment and further tighten the fishing tensioning lines and make
sure the gears are firmly engaged.  (Be careful with pliers; 4# test
will cut easily on steel).

Re-assembly the clutch mechanism , adjust the tension level
settings/bolt to optimal levels as described in the above link, and test
the azimuth with the clutch engeged (tightened); you should now once
again have azimuth control.

Important to remember, run through the drive motor training steps and
reset step as recommended and described by Meade to get the
electronics/drive back in optimum working order/adjustment once the
scope is reassembled completely.

Hope this helps someone out there; I've found the ETX site an absolute
treasure trove of information on this great series of amatuer scopes!

Thank you,

 Chris Scheer
 CSC Computer Sciences Corp.
 GPES UNIX Support Team-Carrier/UTC

Return to the top of this page.

Go back to the Tech Tips page.

Go back to the ETX Home Page.