LX200 Declination backlash elimination

Image 1

In this page you can see the cause and the elimination of declination backlash on the LX200 Meade Telescope.

I have to warning anyone who wants to try these improvements that although the interventions can happens only in the mechanical parts maybe you can have problems in the guarantee terms of your telescope if it is in the guarantee period that Meade gives on its telescopes. 

Also you have to be an experience user and to have a kind of well handling on some basic workshop tools.

And finally I have to declare this is just my opinion based on my experience on my 12" LX200 telescope and I can't guarantee that it can have complete success on your telescope.

First to find out if your telescope has declination backlash just lock the declination knob and then try to move the tube slight back and forth. If you  examine any kind of motion then you have a declination backlash and depend of its amount can cause some problem mainly if you plan to use your telescope for astrophotography.

The cause of the declination backlash has a lot of sources and some of them can be adjusted until to eliminate the problem.

Examine the cause

First you have to remove the plastic cover of declination house system by removing the three allen screw and the declination knob. 

Then check all the topics as I describe it below

1. The Gearing.

The teeth of the worm Gear have fair depth and the gearing with the declination  Gear-wheel must be identical.

But if your telescope is old enough with a lot of used hours it is possible the teeth of the gears to be wearied down making some gap between the teeth.

If you examine this kind of movement , you can do nothing except to replace the gears.

2. Loose of spring load 

Mechanical the declination worm gear system on the LX200 consist of two parts.

The one part is attached to the telescope fork by two screws (Image 5) and the other part is coupled to the first and can be moved up-down loading a spring in order to secure the gearing identical

The gears may be either not exactly rounded or not exactly centered on the shaft and the spring is used because is an identical feedback system to keep the gears in stable force as they are rotating.  

But if the spring load is loose the touch is not identical and can cause a gap between the teethes.

You can examine this by force the moving part down as the arrow in the Image 1. The spring must force back the moving part so the touch of the gears to be complete secure. If this is not happen then you have to unload the spring (position seems in Image 5) and to retention it  dragging it from the edges so to make it more  harden , or if you think you can find a same  new one just replace it.

3. Moving parts coupling

It is the most possible to happen.

The moving part can moved just up-down if you examine any other movement like back and forth then that is the problem. 

The coupling of the stable and moving part is seems to the Image 6 and more details on Image 8 and 9. There are two balls just after the arrows on image 6 and they housed in the correspond hole and are kept tight by an  allen screw in each side (Image 7,8).

The good news is that you can adjust at least the one side of the coupling  and the bad is that you have to remove entirely the declination system.  The other side of the coupling while it is adjustable unfortunately it is not approached.

You can remove the declination system by removing the two screws as in Image 5 and doing this don't forget to unplug the declination cable from the inside fork.

You can then get the entire system on your workshop and to adjust the allen screw 1 on the right (image 7 ) until to have no more movement except the fairly free up-down. You will find a little bit hard to adjust the allen screw and this is because Mead applies the entire screw by appropriate clue just to secure its position. You can do the same after you finish applying an epoxy-metal clue as I did and as you can see on image 7.

4. The worm gear loose.

Again if you examine any kind of unwanted movement in the worm gear except the free rotation by its axis don't worry you can easy fix it. Again as in the case 3 you have to remove entirely the declination system and to adjust the other one screw 2 (the big one on the left in Image 7) until to eliminate the worm gear movement. Be careful you don't have to be excess , the worm must rotate freely and you can examine this by rotating the declination knob.

Prevent it before it happen

As the doctors says the best therapy is the prevention. And there is an important thing that you can do to prevent the backlash on your telescope  and this is the accurate Balance. 

If you stress the motors of an LX200 fork mount system by unbalancing loads can increase by the time the backlash in DEC and RA drive or even can cause motor to fail.

That's all folks about and finally wish you good luck.

George Nikolidakis

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Last edit: 09.11.2000 .