Checkout for Non Goto Telescopes

There are only a few new CAT models available without computers, mostly GEM-mounted scopes like the Celestron Omni XLT, but these also will need to be checked. The usual first step in getting a manual GEM going is installing the RA and declination tracking motors. Since GEM mounts are often sold in both go-to and non-go-to configurations, the manufacturer often packages non-go-to motors separately and leaves it to the user to attach them (go-to motors are most often preinstalled since they are part of a more complex electronic assembly). Follow the manual's instructions for bolting the RA and declination motors in place. Take particular care to make sure the gears that mesh with the telescope's drive gears are properly aligned. Also, be careful that the HC's declination cable goes to the declination motor and the RA cable goes to the RA motor.

The next action for the non-go-to owner is to ensure the mount moves smoothly on both axes. Before beginning, balance the tube in RA and declination following the instructions in the manual and in the go-to GEM checkout section of this chapter. After the scope is balanced, unlock the RA and declination locks and move the telescope on both axes. Movement should be smooth, without any binding.

Most non-go-to motorized GEMs are equipped with slow-motion controls. Before these can be used, a pair of clutches must be disengaged, usually by loosening knobs mounted on the same shafts as the RA and declination slow-motion knobs. Refer to the manual for instructions. When this is sorted out, exercise the declination and RA slow-motion controls. Movement should be smooth and fine. If the scope does not move when a slow-motion control is turned, check to make sure that the RA and declination locks are locked. Next, turn on the power switch on the HC.

Non-go-to GEMs typically feature sidereal speed tracking and one or two higher slewing speeds. When the power is turned on, the mount will be tracking, but it will be moving very slowly (RA drives are often called "clock drives" since their gears turn one revolution every 23 hours 56 minutes and 4 seconds), and the only indication the motor is running will be a faint noise (maybe) and a power-on light. Note that the declination motor will not turn unless the north or south button on the hand control is pressed. GEM tracking only requires the operation of the RA motor.

To check the drive's slewing, make sure that the RA and declination locks are locked, set the HC to the highest slewing speed, and press a direction button. Check all directions—north, south, east, and west (which may or may not be labeled as such on the HC). Motion should be even, and the scope should stop as soon as a direction button is released. Most small-to-medium-size GEMs do display some backlash. When reversing directions using the HC, the scope may pause. Although backlash is not exactly desirable, some is normal in most low- to medium-priced German mounts (and forks). For one additional check, most GEMs are designed for use in either the Northern or Southern Hemisphere, and there is usually a switch on the HC to set the proper direction for RA motor rotation. Make sure this is set to N or S, as appropriate.

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