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How to adjust the Celestron
CG-5 worm gear

 

    For the purpose of this tutorial, I do not recommend attempting this unless you have some, mechanical aptitude.  So, assuming you do, let's get started.

TOOLS NEEDED: #1 philips screwdriver, size 2, 2.5 and 4 metric allen (hex head) wrenches. (and patience.)

 

    First off, unplug all connections to the mount, i.e. the hand control, DEC cable, power cable, etc.  There are three screws that hold the plastic electronics/RA motor housing together.

    One is accessible from the right, at the top of the housing, one fron the left at the bottom of the housing, and the other is in the center, located under the weight rod.  

    The first two are easy, remove them last, the one in the center is a plastic screw, screwed into an insert.  Back the screw out, then use a flat edged tool such as a pocket knife to remove the insert.

     

 

    The plastic housing will seperate into two pieces.  One will come free, the other half, has the small power board attached, and the main board semi-attached.  Pay attention to how the main board is situated inside the housing for re-assembly. 

    Gently disconnect the R/A motor plug from the main board and lay the assembly aside.

 

 

    As the screws to adjust the worm gear are located up and behind the R/A motor, the motor will need to be slid back out of the way, or removed altogether.  

    There is a set screw in the brass cog gear.  To remove it, use the #2 allen wrench.  Then remove the three philips head mounting screws that secure the motor to it's mounting bracket.

 

    After getting the R/A motor out of the way, you can finally get to the three adjustment screws that are located under the worm gear casing.

    

    The screws on the left and right require the 4mm allen wrench, the screw in the center requires the 2.5mm wrench.  

    Before you begin any adjusting, rotate the large brass gear located on the worm gear shaft sevearal turns clockwise and counter-clockwise to get a feel for how much drag there is in the train.  To check for play in the worm gear, gently hold your counter-weights steady with your left hand, while rotating the large brass gear located on the worm gear shaft in a quick clockwise/counter-clockwise motion with your right hand. If it needs adjusting you should feel an "empty spot" in between the clockwise and counter-clockwise motion of the brass gear.  

    If you do not detect any play, leave it alone and put it back together.

    If so, to adjust the play there are three set screws.  

    There is a push-pull interaction between the adjustment screws.

The two outer set screws adjust the worm gear in tighter to the spline on the main bearing.  The center set screw adjusts the worm gear away.

    I recommend making VERY small adjustments as the play may only be a few thousandths.

    First barely loosen the center set screw leaving it lightly seated. Using a clock-face as a reference, adjust the outer two set screws clockwise 1 minute.

    Re-tighten the center set screw, and check the play as was done previously.  If you still detect play, repeat the adjustment procedure again, and re-check for play.

DO NOT OVER-TIGHTEN!

    If after adjustment, you turn the brass gear on the worm gear shaft and it feels a lttle hard to turn, it's too tight.

RE-ASSEMBLY

    Assemble everything back together, making note as you re-install the R/A motor to not get the large and small brass gears too tight against one another. 

    After assembly is complete, fire up the mount and make a few slews in R/A.  If you notice an oscillating sound eminating from the R/A motor, I hate to say it, but you've probably got the worm gear too tight.

    Make the necessary adjustments and re-check.

 

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