ETX-90 EC HORIZONTAL MOTION GEARBOX SHATTERED AND REMEDY Last updated: 23 March 2011

Sent:	Monday, March 21, 2011 03:15:11
From:	James (mephistopheles@rogers.com)
I wanted to share my experience with a recently purchased used Etx90-ec
that I gambled on with the knowledge of its disabled horizontal drive.

I had no previous experience with this telescope and everything was new
and unknown but I took an interest when I came across a deal that was
hard to pass over. A quick survey of the available internet information
about the ETX revealed that drive problems plagued the model but many
people found ways to fix them. So I decided to take a chance knowing
that, at the very least, I would end up with a scope that I could modify
for manual use only.

What I had was the following.

A five or six year old Etx90-ec with a working vertical drive but a
horizontal drive that made unhealthy noises when used. After removing
the bottom cover, I noticed the crack in the gearbox described by the
previous owner and I also realized that an unknown sized piece was
missing and likely fell out when he had opened the bottom to diagnose
the drive malfunction when it happened. Unfortunately, the missing pc
also held in place the first gear driven by the motor wheel. I have a
significant amount of experience working with broken plastic due to my
model hobbies and an early career repairing motorcycle and snowmobile
fairings so I crafted a small part out of some similar plastic which I
glued to the side of the gearbox in order to hold the loose gear back in
place. I accomplished this with the use of a dremel and various bits and
the ever-dependable crazy glue to hold my part to the gearbox.

However, the gears continued to bind up and put too much stress on the
structure which threatened to break the repair that was essentially
working. I found several photos of the gearbox from this site that
indicated I had the correct gear alignment (thank you) so I knew that
something else was amiss. And it was!

The heart of the problem was the worm gear that delivered motion from
the gearbox to the main central gear (the one engaged by tightening the
clutch lever on the outside of scope). The worm gear had a trouble spot
that tightened up with each revolution. I fixed the problem by backing
the nut off by maybe an eighth of a turn which removed the dead spot and
allowed the worm gear to spin freely! Once reinstalled, the gearbox
worked smoothly once again and did not bind up or skip teeth as before!

If anyone finds similar damage with their gearbox, or hears the
intermittant skipping of the gears,  I recommend having a look at the
worm gear! You may be able to fix a problem before it causes the extent
of damage that mine had.

Obviously, the worm gear problem developed over time to the point where
the gears in the box could no longer function normally. And considering
the lack of any replacement parts from Meade, if mine had stripped the
plastic gears, there would have been no repair route available to me
(unless I found an inexpensive way to make new gear wheels).

For now, I have a beautiful new scope that functions perfectly with my
repair!

I can provide some drawings if anyone would like to see how I brought
the gearsbox back from the dead. Just email me with a request for more
info!!

And thank you Mike for your site! I could not have done what I did
without the information I found there!!

Sincerely,

James Elliott

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