ETX TECHNICAL TIPS Last updated: 4 August 2003

Gear Grease Information

Subject:	New ETX-125 with tracking problem -- solved!
Sent:	Sunday, August 3, 2003 02:14:57
From:	stevepur@mac.com (Steve Bryson)
Hi - I thought people may be interested in my experience with my new
ETX-125, in case anyone has similar problems.

Summary: I had no east to west motion on my RA/Azimuth axis at low
speeds.  In particular I had no northern-hemisphere sidereal tracking in
polar mode with the basic EC (though I had good southern-hemisphere
sidereal tracking).  The problem turned out to be grease on the optical
encoder's pink component (It's either the emitter or the detector, I'm
not sure which).  After the grease was cleaned off the telescope works
wonderfully!

Details: This is a story of thinking I had bought a lemon then
discovering an easy but not obvious fix, resulting in a GREAT telescope.

I bought the ETX-125 last week from the discovery store (without UHTC :() 
after waiting several months for the one I ordered -- I couldn't stand
missing Mars anymore.  I should mention that the model I have is the
newer metal-fork model, even though the model number on the box reads
0515-03-01.

The first two nights the autostar behavior was very erratic, sometimes
tracking, most times not.  GOTO on the autostar was often inaccurate. I
reset, calibrated, retrained and realigned the autostar several times,
with no change in behavior.  Then several cloudy days/nights. Today
while doing some Solar observing with the basic EC in polar alignment I
confirmed that it was no longer doing any sidereal tracking at all in
northern hemisphere mode.  Strangely, when I switched to the southern
hemisphere mode it clearly tracked correctly (which is in the wrong
direction for me).  In both northern and southern hemisphere modes the
RA/azimuth motor was making noises so clearly it was trying to track.

After deciding that I did not want to deal with Meade warranty service
(not to mention not wanting to miss Mars) and guided by the wealth of
information on your wonderful site I took a deep breath and opened the
bottom.  The appearance was a little different from Jordan Blessing's
pictures at etxtu.htm, including many
more exposed plastic gears smothered in grease.  I went through his
checklist and there were no obvious problems: the gears were generally
very tight.

I then put the batteries back in the case and plugged in the EC (with
the base still open).  I put it in southern-hemisphere sidereal tracking
mode and could see the gears turning nicely.  Then in
northern-hemisphere sidereal tracking mode the behavior was very
erratic: sometimes there would be no motion of the gears at all, then
after high-speed slewing with the EC the big gear attached to the motor
would wiggle but not turn.  I could find no obvious physical
obstruction.

Inspired by Jordan Blessing's warnings about grease on the optical
encoder gear (which I had verified was clean), I then identified the
three parts of the optical encoder, which is hidden behind the large
gear unlike the photo on Jordan Blessing's site: the toothed gear which
counts the rotations ("counter gear") and is attached to the motor shaft
behind the big gear and is the only gear with no grease; the black
component (the detector?) between the counter gear and the case, and the
pink component (the emitter?) between the counter gear and the motor. 
On close examination I could see that there was a lot of grease on the
pink component.

After removing the batteries, I used a bent paper clip to scrape much of
the grease off the pink component, and a little grease off the circuit
board under the pink component.  It is not easy to see and access this
area because it is under the big gear, unlike the picture of the optical
encoder on Jordan Blessing's page.  I had to be careful not to get
grease on the counter wheel.

After removing most of the grease, I replaced the batteries and put the
system in northern-hemisphere sidereal mode.  The gears now turned very
nicely just like in the southern-hemisphere mode.   I was surprised it
was that easy and my wife was impressed.

Tonight, following Clay Sherrod's excellent instructions on your site, I
reset, recalibrated and retrained the motors using Polaris, then
carefully set home position with a bubble level before doing an easy
alignment.  I then had a very enjoyable 2 hours with the telescope using
autostar in alt/azimuth mode, with rock solid tracking and perfect GOTO
behavior.  I split the double double with a 9mm eyepiece/2x Barlow
(demonstrating the solid tracking at high magnification), and
unexpectedly enjoyed the "best of tonight" tour, with GOTO placing every
object within the 26mm eyepiece field.  I finished with a nice view of
Mars before the clouds rolled in.

If anyone else has a similar problem I hope they find this story useful.
Steve
---
http://homepage.mac.com/stevepur

Go back to the Tech Tips page.

Go back to the ETX Home Page.