This page was last updated on 10/08/14.
DEC Motor Modifications on LX200 - When my DEC motor started experiencing retrograde backlash movement and jumped too much when reversing directions, I decided to make some modifications that I discovered at: http://www.mapug-astronomy.net/AstroDesigns/MAPUG/DecAxis.htm and http://www.mapug-astronomy.net/ragreiner/decdriveadjust.html
I originally started by adjusting the DEC tension screw after re-greasing the worm and worm gear. This got my backlash down to 70 from a high of 85-90, but I ran the risk of binding the motor on some parts of the worm gear while having slop on other areas when trying to get a "single best adjustment." It quickly became clear that I needed the ability to adjust the worm tension on the spur of the moment when imaging in order to eliminate my retrograde and backlash problems.
I have managed to get the backlash setting down to 60 and have eliminated all retrograde motion by "snugging" the tension screw once I am in tracking mode. I still need to retrain the PEC in order to get the most out this tweaking, but everything looks great at this point.
WARNING: This is not for the faint of heart! Do this at your own risk! DEC motors are $150-200. During this modification session I unknowingly broke the solder connection to one of the motors leads while leaving the heat shrink in place (an invisible open circuit). Playing with the wires and hand control I got intermittent operation and tracked the culprit down and resoldered the lead with a hot solder tip. Additionally, the LEDs glue connection came loose and they came away from the gearbox. I got lucky here in that the old glue was still in place so that I could get an exact fit to the original location. I just added another drop of glue once I slipped them back in place and all was well.
(Above Left) DEC motor on LX200 fork. (Above Right) DEC motor w/tension adjuster thumbscrew in place. Notice the small wires going up to the outer left side of the gear box to the LEDs.
(Above Left) The new "instant adjust thumbscrew" (Above Right) Stiffening up the worm assembly to gearbox junction
(Above Left) End view of Adjuster Screw in place. (Above Right) Finger Hole cut into cover for thumbscrew access.