"Re: [M]: LX-200 Classic: RA drive problem on 8" model" in the Meade Astronomy Archive

Subject: Re: [M]: LX-200 Classic: RA drive problem on 8" model
From: Email address hidden
Reply To: mapug@shore.net
Date: Sat Feb 21 01:06:04 2004

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In a message dated 2/20/04 9:00:19 PM Eastern Standard Time,

>
> I have a used (but new to me) LX-200 Classic in 8". The scope was missing
> cords, finder, hand controller, etc. After hunting down parts and setting up
> the scope, everything works fine except for the RA drive (azimuth). Using
> the hand controller, the drive will not move through a full 360 degrees. After
> about 90 degrees the drive starts to labor, slows down and eventually stops.
> Unlocking the scope and returning it to zero (with the lock and fine
> adjustment knob facing the electronic control panel) and then using the hand
> controller starts the RA drive moving again, but it then labors and stalls at about
> the same position.
>
> Similar results occur in GOTO mode, where the Dec moves fine but the RA will
> move to the same approximate location and bog down and then stop.
>
> Any thoughts, comments or help would be greatly appreciated.
>
> Thanks,
> Tom
>
>

Tom,

You've been given some good ideas to check out, so I'll just add a bit to
them. No matter what the problem is, you'll have to take the bottom off of the
scope so as to get to the RA drive mechanics. This is no big deal, though.

Now, when you get in there, look for the foreign objects in the grease as has
been mentioned. But if all looks well, what you want to do is to run the
scope in RA while you're looking in from the bottom and the scope laying down.
Just run it at a relatively slow speed of slew and let it go until it begins to
bog down for you. (You can have the RA clutch disengaged during this so that
the scope won't try to turn on you.)

When you get to that spot, assuming you haven't already seen what the cause
of the bind is already, then put your finger on the gearbox and lightly push it
so that the worm moves away from the worm gear. It should move about 1/8" or
so, but it definitely should be able to be moved.

If you find that you can't get some clearance between the worm and worm gear,
then this is the cause of the bind; they're meshed too tightly. There is a a
set screw that screws in from the bottom of the unit, that pushes the worm
assembly up toward the worm gear. If the screw has been adjusted too tightly, it
causes the worm not to move away.

The whole purpose of this set screw is to allow for some movement, but not to
allow the worm and worm gear from ever completely disengaging. The person
you got this from just may have tightened the set screw too tightly. It's not
uncommon at all for people to adjust this screw and end up making it too tight.
They've perhaps adjusted it because the gears were truly beginning to unmesh,
but went too far. Then, with the temperature change between places where the
scope was used... or whatever... the adjustment is now too tight. If so, then
again, adjust it so that you can get a max of about 1/8" of movement between
the worm and worm gear.

If the person you got the scope from has replaced the RA drive and had
problems with it, then called Meade, they will have suggested that he make this
adjustment because of excess gear slop. As I say, it's not uncommon for this
person to get a bit too ambitious go a bit too far and make it too tight.

Just another thing to add to your possible causes.

But don't get too concerned. There have been many people over time that have
had your symptons, and almost always, one of the suggestions you've received
has fixed it.

If you have any problems with any of the steps, just come back to the group
and there'll be plenty of people that will be willing to help. This group is
like that. <G>

Bruce Johnston
<http://members.aol.com/ccdastro/astronomy.htm>

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<HTML><HTML>In a me=
rites: 
 
 
<BLOCKQUOTE TYPE=3DCITE style=3D"BORDER-LEFT: #0000ff 2px solid; MARGIN-LEFT=
: 5px; MARGIN-RIGHT: 0px; PADDING-LEFT: 5px"> 
I have a used (but new to me) LX-200 Classic in 8".  The scope was miss=
ing cords, finder, hand controller, etc.  After hunting down parts and=20=
setting up the scope, everything works fine except for the RA drive (azimuth=
).  Using the hand controller, the drive will not move through a full 3=
60 degrees.  After about 90 degrees the drive starts to labor, slows do=
wn and eventually stops.  Unlocking the scope and returning it to zero=20=
(with the lock and fine adjustment knob facing the electronic control panel)=
and then using the hand controller starts the RA drive moving again, but it=
then labors and stalls at about the same position. 
 
Similar results occur in GOTO mode, where the Dec moves fine but the RA will=
move to the same approximate location and bog down and then stop. 
 
Any thoughts, comments or help would be greatly appreciated. 
 
Thanks, 
Tom 
 
</BLOCKQUOTE> 
 
Tom, 
 
You've been given some good ideas to check out, so I'll just add a bit to th=
em.  No matter what the problem is, you'll have to take the bottom off=20=
of the scope so as to get to the RA drive mechanics. This is no big deal, th=
ough. 
 
Now, when you get in there, look for the foreign objects in the grease as ha=
s been mentioned. But if all looks well, what you want to do is to run the s=
cope in RA while you're looking in from the bottom and the scope laying down=
.  Just run it at a relatively slow speed of slew and let it go until i=
t begins to bog down for you. (You can have the RA clutch disengaged during=20=
this so that the scope won't try to turn on you.) 
 
When you get to that spot, assuming you haven't already seen what the cause=20=
of the bind is already, then put your finger on the gearbox and lightly push=
it so that the worm moves away from the worm gear. It should move about 1/8=
" or so, but it definitely should be able to be moved. 
 
If you find that you can't get some clearance between the worm and worm gear=
, then this is the cause of the bind; they're meshed too tightly. There is a=
a set screw that screws in from the bottom of the unit, that pushes the wor=
m assembly up toward the worm gear. If the screw has been adjusted too tight=
ly, it causes the worm not to move away. 
 
The whole purpose of this set screw is to allow for some movement, but not t=
o allow the worm and worm gear from ever completely disengaging.  The p=
erson you got this from just may have tightened the set screw too tightly. I=
t's not uncommon at all for people to adjust this screw and end up making it=
too tight. They've perhaps adjusted it because the gears were truly beginni=
ng to unmesh, but went too far. Then, with the temperature change between pl=
aces where the scope was used... or whatever... the adjustment is now too ti=
ght. If so, then again, adjust it so that you can get a max of about 1/8" of=
movement between the worm and worm gear. 
 
If the person you got the scope from has replaced the RA drive and had probl=
ems with it, then called Meade, they will have suggested that he make this a=
djustment because of excess gear slop. As I say, it's not uncommon for this=20=
person to get a bit too ambitious go a bit too far and make it too tight.<BR=
>
 
Just another thing to add to your possible causes. 
 
But don't get too concerned. There have been many people over time that have=
had your symptons, and almost always, one of the suggestions you've receive=
d has fixed it. 
 
If you have any problems with any of the steps, just come back to the group=20=
and there'll be plenty of people that will be willing to help.  This gr=
oup is like that. <G> 
 
Bruce Johnston 
<http://members.aol.com/ccdastro/astronomy.htm> 
 
</HTML>
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