Repairing a Stiff or Binding Dec Slow Motion Knob
There are 3 major causes of binding in the dec axis and we will address all three here. Please take the time to make these repairs if needed and you will be glad you did, the motion will be very even and smooth afterwards.
Cause #1, overtight screws:
We will start with the easiest problem to fix, then we will get in deeper if necessary. The 2 lower screws on the inside of the right fork arm will slightly distort the plastic arm if they are overtightened, this causes the dec screw (the threaded rod between the 2 dec slow motion knobs) to bind. So first try backing these 2 screws out a bit and see if the motion gets nice and smooth. If there is some improvement but not enough, or no improvement then roll up your sleeves and get ready for a little minor surgery.
To repair the other 2 causes requires disassembly of the right fork arm. There are only a few pieces and it is actually very easy. If you have any problems feel free to email me.
Cause #2, Bent threaded rod.
1. Start by removing the optical tube from the mount. This is accomplished by removing the 4 allen screws on the sides of the tube with the wrench that was included with your ETX. Then spread the tube supports slightly apart and pull the tube out the back. This is the worst part of the whole job!
2. Remove the metal cover from the inside of the right fork arm by removing the 4 philips head screws, set the cover aside.
3. Now turn the dec slow motion knob until the round aluminum "drive nut" on the threaded rod is centered. Carefully watch and feel the drive nut as you rotate the slow motion knob, if the threaded rod is slightly bent you will feel the drive nut move towards you and away from you slightly with each revolution of the rod. If this is the case turn the knob till you feel the nut come towards you, at the point where it is most towards you stop. Now give the nut a gentle but firm push away from you to bend the rod in the opposite direction. Repeat this process as many times as is necessary until you are satisfied that the rod is very straight.
Cause # 3, Tangent arm to "drive nut" fit is too tight.
If you are still not happy with the motion there is one final culprit (and it is usually the MAIN CAUSE of dec stiffness and binding). The culprit is a very tight fit between the tangent arm "fork" and the drive nut. This prevents the drive nut from moving easily and changing its angle as needed. To repair this we will have to do just a little more disassembly.
1. Grasp the Meade Logo trim ring and unscrew it totally, remove it along with the setting circle.
2. Loosen the dec lock knob.
3. Pull the tube support out from the inside of the fork and set aside. Notice that there is a black plastic bushing/spacer that may be on the tube support or still in the fork, get it and set aside.
4. Grasp the tangent arm (the piece that runs from the lock knob down to the threaded rod) and remove it by pulling upward to disengage it from the drive nut.
5. Now look at this arm. You will notice that at the bottom there is a small "fork" that fits over a groove in the drive nut. This is where the problem lies, this fit is too tight. While you don't want it real loose and sloppy you don't want it bindingly tight either.
6. You will need to take a piece of sandpaper or a razor knife and remove very small amounts of material from either side of this fork until you get a nice fit that slips over the nut without any binding whatsoever. After the fit seems good reassemble the tangent arm and check its operation.
7. If all is well the knob should now turn very easily throughout its entire range. Assemble in reverse order, remember when reinstalling the metal cover be sure not to overtighten the 2 bottom screws (just barely snug is good).
If you have any questions please feel free to email me, just describe everything as carefully as possible.
Email: jblessin@worldnet.att.net