ETX-125 PE SMARTFINDER - LNT MODULE REASSEMBLY Last updated: 9 March 2009

Sent:	Thursday, March 5, 2009 07:45:31
From:	raydeasy (raydeasy@mindspring.com)
I concur with everyone who mentions that you have a really useful site
full of tips and technical information.  I have visited from time to
time for many years.  I bought an ETX-125 PE several years ago, but due
to health issues never got to use it.  I am now in the process of
getting it up and running.

Because information was being lost between sessions, I knew I needed to
replace the battery in the LNT Module.  After doing so I went through
the routines of Sensor Calibration, Motor Calibration and Motor
Training.  I performed all of these during daylight hours.  I finally
got to the after-dark chore of aligning the SmartFinder with the
telescope optical path a few nights ago.  However, I could not see the
red spot on the lens, but I could see the red LED shining under the
bottom edge of the cover of the LNT Module.  This was a tip that I
overlooked for a couple of nights while fiddling with the two alignment
screws.

Last night I removed the LNT Module cover again and took a look at the
assembly that pipes the light to the little lens sticking out the side
of the LNT Module cover.  It immediately dawned on me that the end of
the optical fiber should not be just dangling.  The end of it has a
little hood.  It was obvious that the little hood should be pushed over
the bulb of the LED.  I did so and reassembled the unit and it then had
a red dot projected on the lens of the SmartFinder.

The springs are a pain, but reassembly is easy if you put a very small
dab of adhesive caulk on the end of each one and shove it into the place
where it belongs.  Do not use so much caulk that you cannot run the
screw through the spring.  Let it cure for a few hours or preferably
overnight.  You will not have to be a contortionist with petite fingers
to get the side spring in place after that.

Begin reassembly of the unit by tilting the LNT Module cover down at the
back.  Reach in and push the hood at the end of the fiber optic assembly
over the LED bulb.  Then tilt the cover  forward using care not to pull
the fiber optic hood off the LED bulb.  When it is in place, insert the
side alignment screw and tighten it enough that you can see the end
starting to come out the opposite side.  Insert the top alignment screw
and tighten it a few turns.  You are now ready to go out and get it
aligned with the telescope optical path.

I hope this tip will help people who cannot see the red spot on the lens
after replacing the LNT Module battery.

Thanks again for keeping this informational site active all these years.
 
Ray

Subject:	ETX-125 PE SmartFinder - LNT Module Reassembly 
Sent:	Monday, March 9, 2009 06:56:07
From:	raydeasy (raydeasy@mindspring.com)
This is a continuation of my discussion of reassembly of the LNT Module
after replacement of the battery.  In my case after reassembly the red
dot was dislocated to the extreme left edge of the lens and it was
impossible to move the alignment far enough to agree with the telescope
optical path.  I disassembled it again in hopes of seeing something I
had overlooked, but found nothing obvious.

Caveat Emptor: However, reassembly a second time proved disastrous.  The
strain relief on the tube which contains the optical fiber pulled out of
the slot on the side of the LNT Module cover, thus pulling the optical
fiber out of the hole in the side of the cover.  It is held in place by
a gooey substance like thick syrup.  I spent the next two nights making
multiple attempts at getting the short length of optical fiber through
the hole and then shoved back into the tube far enough to pick up the
output of the LED.  The optical fiber also has the gooey substance on it
inside the tube.  I was totally unsuccessful.  I gave up.  I also
decided I did not want to deal with the sometimes less than responsive
services provided by Meade to obtain a replacement LNT Module.

I had previously read an article on your site the mentioned the use of a
BB gun red dot sight as a substitute.  At a local sports shop I selected
one that had a crosshair on the lens at the front.  The cost was about
$10.  I removed the SmartFinder lens and decided to mount the BB gun red
dot sight along the same approximate line used by the SmartFinder.  To
do so, I removed the clamp pieces that clamp the sight to a rail mounted
on the guns.  I used double-sided tape on the bottom.  However, after
mounting, Sensor Training showed the initial sensing of North to be off
by more than 20 degrees to the East.  Because the BB gun red dot sight
was a cast plastic unit except for the rail clamps which I had removed
and the adjusting screws, I immediately suspected that one or both of
the adjusting screws were magnetized which would screw up the sensitive
sensor in the LNT Module used to sense the earths magnetic lines .

Without removing the BB gun red dot sight, I removed the horizontal
adjustment screw from the unit.  The next attempt at Sensor Training
showed that the North sensing was pretty close.  I decided to pull the
unit and go to a hardware store and buy substitute nylon screws and
nuts.  The original screws were metric size M4 x 0.7 mm.  Local hardware
outlets did not have metric nylon screws and nuts.  I could wait a few
days and get them from a source like McMaster-Carr, but I decided to get
8-32 nylon screws and nuts and tap the existing holes up to that size. 
The plastic adjuster has a vertical and a horizontal hole and with very
little effort the holes were re-tapped for 8-32 screws.  This picture
illustrates the result of the effort.  A second nut was used to lock the
one pulled up to the edge of the housing.  The double nuts are also easy
finger grabs for adjusting the unit.  One double nut is installed on the
left and the other on the top.  The screws were excessively long and the
extra length was snipped off close to the lock nuts.  This picture shows
the result.



Approximate alignment of the unit with the optical path of the telescope
is easily accomplished by first removing the cover from the corrector
lens and laying a level on top of the unit.  The cover has a slightly
larger diameter than the OTA.  This picture illustrates this step.



Next use the level along the line where it is desired to place the BB
gun red dot sight.  Use a strip of masking tape along the edge of the
level to set the line.  Ensure that the selected location will not
interfere with the use of imagers.  Additionally, if a hard case is used
ensure that the foam in the cover is cut away to accommodate the
placement of the BB gun red dot sight.  This picture shows a method of
making a guide line with masking tape.



Finally, place the BB gun red dot sight along the edge of the masking
tape.  The particular BB gun red dot sight I selected had a lot of both
vertical and horizontal adjustment and probably could have been placed
by eyeball and still been able to be aligned with the telescope optical
path.



One oddity of placing the BB gun red dot sight down around the
circumference of the telescope and not on the top center line is that
the crosshairs are tilted counterclockwise.  I decided that mainly I
just want the target inside the small inner circle and on the crossover
point.  Even with a 6.4 mm reticule eyepiece sighted on an electrical
insulator on a utility pole about 1.5 miles away, I was able to easily
get the red dot on the crossover point and aligned on the insulator. 
Although there is a small shield around the lens, in bright daylight you
will need to hold your finger or something dark in front of the lens of
the BB gun red dot sight to see the dot.  Just by moving a finger into
and out of the line of sight as I was adjusting, it took only a few
minutes to get it extremely close.

There seems to be a little tinting on one side or the other of the BB
gun red dot sight lens and due to cloudiness it has not been tested at
night to see if that interferes with sighting on reasonable magnitude
stars ... maybe down to magnitude 3 or so.  For now this looks like a
quick, easy-to-do replacement for the SmartFinder.
 
Thanks again for the informative site.
 
Ray Deasy

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