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Last updated: 27 August 2013

ETX-90EC DEC fix

Subject:	 Reducing dec axis backlash
Sent:	Sunday, July 4, 1999 11:44:49
From: (Jerry Tietz)
In the process of replacing a broken dec axis bracket I discovered that
the dec motion backlash is greatly reduced if the thin metal disk in
back of the screw-on dec lock knob is removed. You might try this to see
if it works since it is so easy to do.

Jerry Tietz, Ph.D.
Psych. Dept.
Univ. of CA
Santa Barbara, CA 93106

From: Tony von Ruden (

The right tube adapter failed on my ETX-90EC for the SECOND time
yesterday, and exasperation being the true mother of invention, I think
I up came up with a solution to fix the problem once and for all.

Last time it failed, the shaft sheared off at the edge of the press-nut.
This time, mercifully, the press-nut simply came loose, leaving me with
something to repair.  The 1/4" hole that the press-nut fits into is 3/4"
deep, although the nut itself is only 1/4" high, and with the knurled
length only about 3/16" long.

After a trip to the local hardware store, I made myself a brass
replacement that is 1/4" outside diameter X 3/4" long, with a 10-24
thread tapped all the way through.  I cleaned the new threaded insert
and the hole it would go into with isopropyl alcohol, then used 5-minute
epoxy to glue the insert into place.  I added extra epoxy to the bottom
of the hole in hope that it would ooze up into the lower threads, adding
some extra holding power.

The new assembly seems to work like a charm. The bond between plastic
and metal is now at 4 times the area, and is adhesive as well as
mechanical. The stress concentration caused by the edge of the press-nut
has been eliminated, or at least moved down to the base of the hole,
where the stress can be distributed throughout the face that supports
the gear.  I estimate the repaired part is at LEAST 10 times the
strength of the original.  Time will tell -- I'll keep you informed.

I'm including a photo showing the new new part next to the old, before

DEC fix

The photo also shows the clutch assembly, for the benefit of those who
haven't yet had theirs fall apart.  The cast iron drive gear is
sandwiched between the black plastic right tube adapter (RTA) and a
black plastic hat-shaped piece (HSP). The shaft with keyway and threaded
insert (missing in photo) is part of the RTA. A white plastic bushing is
in place over the HSP in the photo, but you can see the top, keyed edge,
and the bottom face next to the gear. When you tighten the DEC clutch
knob, you are pulling on the insert and RTA, and pushing on the HSP,
squeezing the gear -- it's a simple friction clutch. The HSP has a tab
sticking out of it that hits the limit stops molded into the housing. 
It is keyed to keep it from rotating with respect to the RTA.

Well, enough messing around with the hardware -- It's time to try
upgrading my Autostar firmware.  Thanks again for maintaining your
terrific site!

Tony von Ruden

Subject:	RE: Meade ETX-90/EC Right Tube Adapter
Sent:	Friday, March 19, 2010 07:46:12
From:	Tim Magrino (
I wanted to follow up and let you know that I was able to repair my
right tube adapter following the procedures from your site with some
slight variations.  The whole thing cost me 48 cents in parts, which was
a lot cheaper than the $165 that Meade wanted to repair the telescope.

Since the shaft of the tube adapter was sheared off at the base, I had
to drill a hole completely through the shaft and screw a 1/4 inch
furniture fastener with a 8-32 screw hole into the broken end of the
shaft.  The furniture fastener screws into the plastic shaft with an
allen wrench, so you have to secure the shaft somehow while screwing in
the fastener.  I held the shaft with a pair of pliers with a towel
between the shaft and the pliers to prevent the shaft from getting
damaged. I also had to trim off a triangular shaped piece of plastic
from the inside of the tube adapter base to make room for the screw.  I
used an exacto knife to trim the plastic. That allowed me to secure the
broken shaft back on to the base by screwing them together.  I didn't
use any glue because I was afraid of getting glue in the threads of the
brass fitting on the other end.  The repair seems pretty solid without
using any glue.  I bought the 1/4 inch furniture fastener and 8-32 screw
at Ace Hardware for a total of 48 cents.

I hope this information will be helpful to anyone else that needs to
repair a broken right tube adapter.  I am including a picture of the

Thanks for your help.



Subject:	ETX-90 Alt/Dec Clutch Repair/Enhancement
Sent:	Friday, April 30, 2010 08:18:23
From:	Nohr Tillman (
I bought my ETX-90 used, and it has exhibited not-so-good clutch
clamping with the Altitude/Declination fork arm. Knowing this is a
common thing, I disassembled the scope and arm to improve this clutch
mechanism. The "clean and sand the surfaces" approach had been performed
before I got the scope, and I found the plastic arm surface was not
sanded uniformly. So the gear did not seat on the surface perpendicular.
It did not have good grab at all even though the surfaces were clean and
free of grease.

Pictures are worth a thousand words so I'll let these two do most of the
talking. In short, I trued up the plastic surface some with automotive
valve grinding compound between the gear and the arm surface. After
cleaning that off with alcohol and soapy water, I expoxied the
overhead-valve spring shim (1.25 dia X 0.15 inch thick) to the arm. This
further fixed the flatness and turned the clutch into a true friction
clutch with the effective clamping surface at the outer diameter. It
works very well with much less clamp load required to positively lock
the arm to the gear.
Hope this helps someone else too,
Nohr Tillman
Troy, MI, USA, Earth



Subject:	ETX -90EC repair? [NEW!]
Sent:	Monday, August 19, 2013 13:55:06
From:	Ned Thanhouser (
Hi, I have a ETX-90EC and the vertical declination gear or pulley belt
seems to be broken (I.E. no resistance or motor drive in this axis).
Mead reports no support. Recommendation? Thanks. Ned

Connected by DROID on Verizon Wireless
Mike here: It sounds like the Right Tube Adapter is broken. You may be able to repair it yourself. See the article "ETX-90EC DEC fix (Right Tube Adapter repair)" on the Helpful Information: Telescope Tech Tips page. Alternatively, you can contact Dr. Clay Sherrod for his Supercharge Tune-Up Service (link on the ETX Site home page).


Thank you so much...I shall endeavor to fix it.


Disassembly reveals the problem as described in the article you referred
to below "ETX-90EC DEC fix (Right Tube Adapter repair)."

The DEC shaft is sheared off at the edge of the press-nut. See attached

The fix appears to be to just epoxy these two parts back together...yes?
But I am very concerned about getting epoxy where it shouldn't and
bugger the whole assembly.

I don't need a new bushing as it is still secure, although Tony von
Ruden's solution appears more robust with the longer bushing.

Can you please confirm? Any where to get a new part?

Thanks so much for your help!
Mike here: Epoxy may work although there is a lot of torque there. You might try Telescope Warehouse (link on the Astronomy Links page) for a replacement RTA but I doubt he has any without purchasing a new mount.


Thanks for the suggestion, I'll keep you posted. Ned

And an update:

Hi Mike, thanks for all your helpsince the RTA sheared off flush with
the original press nut (right in pix below), I was able to find a
replacement 1/4" x 10-24 press nut ( that
is 3/8" vs. 1/4" deep with flanges that fit into the RTA (with some
persuasion) into the tube below where it had sheared off. That plus some
5 minute epoxy seems to have done the trickeverything works now and I've
added a note on the instrument reminding me and others NOT to over
tighten the clutch! Thanks below for your help and excellent site. Feel
free to post.


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