TECHNICAL TIPS Last updated: 25 February 2002

Repairing a Binding Right Ascension (Azimuth) Axis

Subject:	Repairing a Binding in an ETX-125EC RA Movement
Sent:	Friday, February 22, 2002 21:11:30
From:	jchalfen@attbi.com (John Chalfen)
Mike, you asked me to keep you updated if I split the base. Well, I
split it.

First off, on examining the big nut, not only is there lok-tite in
there, but a healthy dose of grease. Cleaned the whole nut shiny as new.
Cleaned the threads on the shaft while I was at it.

Checking the stop ring and the teflon ring showed lok-tite, grease,
metal filings....Basically a lot of crud on the two rings. Cleaned the
rings and the whole path thru the shaft opening. Stopped the crud
leakage....

I now have the base spinning like it is on ice. Until I put the nut back
on. Looking at the nut, and where it meets the base at the shaft, there
is a divot on the base and a corresponding burr on the nut. So it looks
like it may be slightly damaged just under the nut. Still checking it
out though, and I'll let you know what the final answer is. If I can
come up with one. Maybe just have to live with it binding at the stops.

Tough to find, but I got it figured out. Here goes if you are ready:

Under the big nut is an assembly which houses a sleeve on bearings to
allow the base to rotate around the shaft. The assembly housing is
aluminium (I believe) and held in place by a ring. Apparently when this
scope was assembled, the nut had been over tightened. That was the main
binding issue. The reason it was binding at the hard stops is actually
pretty simple after I thought about it and looked carefully.

Due to being over tightened, the nut bent the sleeve housing barely
noticeable. Since the nature of threads and nuts is such that the nut
doesn't sit level, it actually sits at a small angle, the bend or rise
(if you prefer) in the housing would only contact the nut at one spot,
near the hard stops.

My solution is to hand tighten the nut so that it just secures the base,
but still leaves it loose enough to where the bind is almost negated. So
far it seems pretty slick and turns *really* nicely.

I do however have two questions that I hope Mr. Sherrod can answer (or
anyone who may know, I'll take any answer). First is the stop ring: Is
it supposed to be pushed by the pin(s) all the way around in a full
circle? (Seems right the way it's acting). I tried it with the "V" on a
pin, but it didn't seem right.

Second question: the DEC and RA connectors pulled off the PC board
before I had a chance to note their position. Black wires face left or
right? (left being the edge of the board, right being away from the
edge) I Know which connector goes where, just not the correct
orientation.

If you want pictures of  the shaft sleeve and such to make it clearer,
let me know and I'll send some. Hope nobody else has this problem, it
was a bear. It wasn't a waste of time though, learned a lot about how
they put these things together. It's pretty neat!

jchalfen@attbi.com
jchalfen@aol.com

In the one picture:

1 = Retaining ring
2 = Shaft housing
3 = Shaft sleeve

Above the 3 you can see the dent/ding from the nut. (The nut also had a
burr on it, as if someone slipped with a tool. That's what made the
dent.)

The other picture is a different view, with the dent/ding above the D.

If you (or anyone) would like any other pictures of the inside of an
ETX-125/EC base, let me know. Mine is going to be apart for a week or
two as I need to repair the wires I cut before I fully assemble the
base.

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