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c8 repair – opening the base part 1 June 2, 2009

Posted by aquillam in Astronomy, telescope maintanance.
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This post is one in a series about C8 repair and maintenance.  You should see the introduction and disclaimers before trying anything here.

When mounted on an equatorial wedge, the telescope rotates in right ascension (RA) through the motors and gears in the base. To address issues with the RA lock, RA fine motion, and tracking you’ll have to open it up. First of course, you should eliminate any other problems, like making sure the RA lock lever is adjusted and the wedge is polar aligned. Please make sure you’ve eliminated all other possible problems before you open up the base! If you’re sure you have to get in there, it is best to have help.  There are a couple steps here that are a lot easier if you have an extra hand.

Remove the arms

This is probably the most dangerous part, because it is so easy to drop the OTA while doing this, so this is the most important part to have an extra pair of hands.

The arms are held to the base with two allen-head bolts each.

Two allen-head bolts hold the arm to the base

Two allen-head bolts hold the arm to the base

I like to loosen all four of the bolts slightly, then remove one from each side, then the other one. Make sure the OTA is secure before removing any of the bolts! It won’t matter if the RA lock works if the corrector plate is broken. And I’m pretty sure breaking the primary is an automatic lifetime of bad astronomy luck.

I like to put the bolts together in a piece of masking tape and tape them to one of the arms so they stay together.

Remove the cover

With the arms off, you can remove the cover. On some models, this is a plastic piece you remove by slipping something like a jeweler’s screwdriver under the edge.  On this scope, it is held on by 3 medium sized allen head bolts.

The cover plate is held on with 3 allen-head bolts

The cover plate is held on with 3 allen-head bolts

Again, I tape the bolts to the bolts to the cover to keep everything together.

With the cover off, you can see the cap that actually holds the base together.

The cap under the cover

The cap under the cover

Remove it with a small allen wrench (why are they all different sizes?!?)  With the cap off you can see the top bearing.

the base with the cap removed

the base with the cap removed

Separating the covers

Lift the top of the base off the round bottom part.  The easiest way to do that is for one person to hold the bottom and the other person to lift on the rectangular top. Sorry, but I couldn’t take a picture of this… The RA dial and gears will come off with the top half.

Inside the base

Inside the base

From here, you may want to go on to:

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