Repairing the Dec/RA drive.

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Supplemental tips

Tip #1

This isn't directly related to having to fix anything inside the Dec or R.A. units, but has to do with having to adjust the screw on the R.A. unit that controls the distance the separation between the worm and worm gear. If the spacing is too small, the gears may bind at certain points in the cycle. If it's too great, the gears may separate too far and the gears may unmesh.

The strange part is, the scope may be working fine for quite some time, and suddenly conditions occur where this distance must be adjusted. Unfortunately, to get at the adjusting screw, you must remove the drive base cover, then remove the R.A. gear assembly, then make an educated guess on whether or not the adjustment is correct. After re-installing the gear box, you can see if the clearance is right, but if not, out comes the gear box and some tweaking of the adjustment screw is done, then it gets re-installed. Pain in the neck!

This tip may save some of this hassle in the future.

Once the unit has been opened and the R.A. unit removed, rotate the electronics board 90 degrees if necessary, so as to gain access to the adjustment screw from the bottom of the unit. Then remove the allen screw and replace it with a long, plastic or nylon screw of similar thread type.

When I did this, the only available plastic screws were too short for my purposes, so I also bought a plastic hex coupler that allows two screws to be joined together. Cut both of the heads of the screws off and couple them together, then thread one end into place.

A nice little 'handle' for the screw can be made, by buying a 'twist on wire connector', used for manually splicing or connecting two wires together. There are sizes available that fit on the nylon thread with no extra work.

You now have a long screw that can be threaded into the adjusting screw hole, and can be accessed in the future by simply removing the screws from the control panel and lifting it out. The screw can then be adjusted by your fingers as needed while the scope is still mounted on the wedge or tripod.

As I said, this is nothing earth shattering, but it may help you in the future.

Note: If you find that you need to make the screw adjustment because there is a 'tight area' on the worm gear, then whether or not you make the adjustment, you still have a condition that will effect the 'GOTO' accuracy of your LX200. You might want to go to the following link, to aid in correcting this 'Go To' problem. <Improving `Go To' accuracy on the LX200>

Tip #2

Here's another change in the same area that might be of some benefit to you.

It seems to often happen that you may find that for whatever reason, the spring tension on the spring that meshes the worm to the worm gear on the R.A. drive, has changed, or just plain needs better adjustment. As with the previous tip, it means removing the bottom of the scope, then the R.A. drive unit and either compress or expand the spring to change the tension. Then you put the gear box back in and try it. Again, a pain in the neck. That's especially true if you have to 'guess' at the amount of spring tension you really need, and do it several times.

If you want to take the time to make the following modification, then as in tip #1, you can simply unscrew the four screws holding the control panel in place and reach in to adjust the spring tension.

The upper left image shows the area in which the tension spring sits. It sits in a recessed hole in the bottom plate of the unit and pushes up against the upper unit. Drawing '1' shows only the lower plate .... the part needed to be modified ... and the recess in which the spring sits.

In drawing '2' you can see by the larger red circle, that I milled the recess a bit larger. The smaller hole, the red one right in the center, is where I drilled and tapped a threaded hole so that it would accept the same size of nylon screw as was used in tip #1.

Drawing '3' is a side view of the newly enlarged recessed hole and the small tapped hole. As you can see, there is a significant clearance now, between the side of the new recess, and the original spring.

In drawing '4', you can see a small 'cup' that I made. This is just large enough to freely fit into the new recess. Also, there is a hole in the middle of the bottom of this 'cup' that is even smaller than the tapped one previously made in the metal plate. This 'cup' was made so that the original spring could nicely sit inside it. Using the resulting size if the 'cup' is how I determined just how big to make the recessed hole. I wanted the 'cup' to freely sit inside of it. This 'cup' looks like a miniature bottle cap.

In drawing '5', you can see that I took one of the nylon screws and filed a portion of the end of it down. I made it just small enough so that the reduced section would fit into the hole drilled into the 'cup' with a portion of the tip extending up and into the 'cup'

In drawing '6, you see it all put together. If the screw is screwed in, it raises the 'cup', which pushes the spring up, where it is compressed against the upper section, increasing spring tension. If screwed down, it reduces the spring tension that is meshing the worm and worm gear together.

A nylon screw is used in both tips, because we don't want any metal down in the area of where the wires and connectors from the control panel when it's back in place. Just as in tip #1, one screw wasn't quite long enough. On this one, I just took two screws and locked them together by screwing them both into a single nylon nut and tightening them to quite snug. Either method will do.

I trimmed any excess length off of the screw and put the control panel back in place. Now, I can make either of the adjustments as I wish, without dismantling the scope. Just pull the control panel, reach in, and tweak away!

Closing thoughts.

You've covered a lot of territory if you managed to follow this discussion from beginning to end. Hopefully, the journey was worth the effort, and hopefully, there will now be a LOT fewer people that will have to send there electronics or 'scope in for repair from now on.

As time passes, I hope to add more ideas and tips on how to fix problems related to the drive electronics and mechanics. It's really surprising how a unit that only measures about 4" x 2.5" x 1.5", with a circuit board that's only about 1" x 1.5", can be the cause of so much frustration and so many problems, but I guess that's just a part of the hobby.

Best of luck, clear, dark skies, and....................................................................

Enjoy Astronomy!!!!!!

Bruce A. Johnston

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