Meade LXD75 mount backlash fix.

Source: https://www.cloudynights.com/topic/22630-lxd75-backlash-adjustment-in-ra/#entry763612

I had the same problem with my new LXD75. There are two Backlash souces; Worm Mesh and Worm Shaft.

Do this adjustment without OTA or Counterweights!

Remove RA Motor assembly, by removing the single Metric Allen which goes through a slot in the main mount, above the Lattitude adjusting screw, below the Polar Finder.

Observe the Worm Gear housing with the shaft and aluminum gear. Rock the backlashing mount and observe if this shaft moves in and out of the housing with the backlash. If so, then you have shaft backlash.

If you rock the backlash and the shaft is not moving, you have gear mesh backlash.

Correcting Shaft Backlash:

Remove the 17mm Brass Hex Nut from the worm gear opposite end from the aluminum drive gear.

Tighten the internal brass piece with your fingers, all the while rotating the aluminum gear with your other hand until the backlash is gone but the gear turns freely.
Reinstall the nut and tighten lightly, still checking for free rotation on the aluminum gear. Repeat several times if necessary until there is minimum backlash, nut is tight, but worm shaft still turns freely.

Correcting Mesh Backlash:
There are 3 Metric Allen screws on the bottom of the worm gear housing. The outer screws pull the worm closer to the ring gear, while the center Allen pulls back and locks.

CAUTION: THESE SCREWS ARE THREADED INTO CHINESE MELTED POP CAN ALUMINUM, AND A LIGHT TOUCH IS REQUIRED!!!

Loosten the center Allen and tighten the outer screws equally a little, then retighten the center. Test and Repeat until the worm mesh backlash is gone but again the worm turns freely.

When complete, reinstall the motor housing but before doing so, check and see if the brass gear on the motor and the aluminum worm gear are actually installed with the gear setscrew on the flat of the shaft (none of mine were)
You will need a 1.5mm Allen (0.059in)for this, although you may get away with a 0.050 US key for one or two times.

Align the motor housing to mesh the gears. These gears are a wonder of Chinese Manufacturing, having been individually carved from manhole covers with an axe and a rock. They hav absolutely no “Gear” shape to the teeth, and are not even circular. If’d meshed fully, they will bind and burn your motor.

I found having the AutoStar working on #4 speed, and adjusting so that a piece of copy paper goes between the gears with marks but not quite cut through is about best.
Your motor sound will tell you.

Enjoy

Karl
kpoirier01@rogers.com