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Disassembly Pictures for NexStar 5/8/5i/8i Altitude Axis

In chapter 12 of the NexStar User's Guide I describe how to disassemble, reassemble and adjust the NexStar 5/8/5i/8i mount.  I included as many pictures as was practical for a book, but thought additional pictures would be useful.  Note that the book describes more detail; these pictures are meant to supplement.

Caution! The very real possibility exists during the procedures described here that you may damage something. Also, disassembly may void your warranty and you should consider returning your telescope for warranty work rather than attempting adjustments on your own. After the warranty has expired you should consider the possibility that you will cause costly damage when working on your scope. While I consider the following procedures reasonably safe, not everyone should approach an expensive piece of equipment with a screwdriver in their hand.

The pictures below were provided by Brian Schilt, Ray Cooper and Frank Dilatush - thanks guys! 

Click any of the pictures for a larger version.

In this view, the hand control has been set aside revealing the cover for the altitude axis nut.  Remove the three small screws to free the cover.  Use care to prevent the screws from falling down into the base - it is best to lay the mount in its side to prevent this.
After removing the cover, the nut is now visible.  Before removing, keep this in mind - after removing this nut, the optical tube is free to fall from the fork arm - you must support the optical tube and remove it to safe place after you remove the nut, bearings and washers.  Also, prior to loosening the nut, it is a good idea to mark the nut and the shaft with a permanent marker to help with adjusting the correct tension upon reassembly.
Celestron has used different combinations of washers throughout the production of the 5/8/5i/8i series.  You MUST lay these parts out in the correct order when disassembling to insure you replace them correctly when reassembling.  A quick sketch or photo is advisable in case the parts get moved while you are working.  The photo at the left is a typical arrangement - the large washer to the right goes back on first and the large nut goes on last.  The cone-shaped washer (large side down) goes on just before the nut.  If there is a second flat washer, it is placed between the bearing and the cone-shaped washer.
When you remove the OTA, the large gear and three nylon disks shown here will either come off with the optical tube or remain in the top of the fork arm.  They are loose, so set them aside to prevent dust from accumulating in the grease.

When you pull free the gear, you will find a black disk between the gear and the bracket (the large silver surface shown in here).  This disk provides the friction that actually drives the altitude axis up and down.  Be sure to keep the bracket and the side of the gear free from grease on the surfaces that mate to the black disk.
This photo shows the track that the three nylon disks ride in.  Upon reassembly, be sure to place the nylon disks in the recesses in the large gear so that they will ride smoothly in this track.

After reassembling all the parts, to correctly adjust the tightness of the nut, first tighten the nut to line up the marks made as suggested above.  Push down on the front of the scope. If it moves too easily (some experience will be called for), tighten the nut a bit and try again.  Too tight and the mount may not move freely, tracking will suffer and battery life will be shortened.  Apply power to the mount and ensure free movement.  Adjust the nut again if necessary.

See The NexStar User's Guide for more details on adjustments, cleaning and lubrication of the axis.

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Michael Swanson
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