LX90 Dec pointing out by 4 degrees over run

The main problems encountered with the mechanics of the telescope centre around the mechanical swarf, grease compound, the liberal use of grease and the quality of machining of the main DEC and RA gears.
1. Remove the motors from the telescope. Be careful when removing either motor as there is a compression spring between the motor mounting frame and the worm shaft assembly.
The RA motor is located under the telescope body, removing the 4 screws and 2 Allen bolts will allow the bottom cover to be removed, thereby allowing access the the 2 Allen bolts holding the motor in place. Unplug the motor from the main PCB before removal.
The DEC motor is in the the fork arm containing the clutch and fine DEC adjustment control. (Never to be used with power applied to the scope). Remove the 3 small Allen screws holding the plastic cover plate in place and the DEC clutch knob to allow access to the motor. Remove the RJ45 connector located inside the telescope fork arm. Then remove the motor by unscrewing the 2 Allen bolts holding the motor in place.
2. Remove all grease from the motor worms, especially around the RA motor's magnetic pulse detector and the permanent magnet built into the worm shaft.
3. Remove all grease from the main DEC and RA gears, making sure to clean into the gear teeth.
4. Lightly re-grease with a Molybdenum Disulphide based grease (Castrol MS3 is great for this application if you can get it)
5. Assemble in reverse order. But before doing so, carry out the electrical adjustment above then, (a) relocate the the RA and DEC control PCB's in the vertical plane thereby gaining access to their respective backlash Allen screws. Adjust for 20thou max clearance when in final position. Note:- the DEC adjustment screw has to be replaced for a longer unit complete with a thin bolthead as this adjustment has to be carried out with a spanner....there is no room for an Allen key adjustment here.
6. A drop of Loctite must be applied after adjustment.
7. The final part of the process is to run in the gearing. Apply 12 volts to the motor wires, either at their respective plugs or to the motor direct. Allow to run for 2 to 3 hours in each direction by reversing the battery polarity to bed the teeth engagement. Remember to release the clutches.

Your DEC is the same as your Latitude--

Right Ascension does not matter for now. Polar Align the scope on the star Polaris-- read this:

http://arnholm.org/astro/polar_alignment/index.html

Once you are polar aligned, rotate the tube to a star in the sky that you KNOW the name of. Look up the Right Ascension of that star on a cell phone app or a laptop planetarium program like this one:
www.stellarium.org

Rotate the RA setting circle so it matches what the phone or laptop indicate. LOCK down the RA circle. Your scope is now adjusted to the sky and you can use the numbers on the DEC and RA to find other objects of known RA & DEC.


www.telescopeman.org
www.telescopeman.us
www.telescopeman.info

Once the scope is polar aligned move it to a named star that you can identify. Look up the RA and DEC for that NAMED star in any planetarium phone APP or a laptop running any planetarium software like the free software available at www.stellarium.org

Adjust the circles to MATCH the RA and DEC in the planetarium software, and lock them down.

Now you can use them to find other objects of known RA and DEC.

Since you already disassembled the scope-- you can send the board to Ron Sampson and he should be able to repair it. He fixes main boards and hand controllers (including the screen and keyboard on the hand controller!)

If you post a message on the Yahoo LX90 group looking for Ron Sampson he will answer you. You can then email or phone him for instruction on how to send him the board.

ARE YOU SURE it's the board? It could be a bad keyboard or a bad cable on the hand controller. You should get another hand controller and cable and test it before you send it off. Can you borrow a hand controller and cable from anyone.... or from a local scope retailer?

The clutch is not engaging in RA. Maybe the gears are not actually meshing together? A loose worm gear?

You can open it up and look and see if anything obvious is loose. Otherwise it's a trip back to Celestron.

It assumes you are in POLAR mode, and polar aligned. Only RA is needed to track the stars.

Look at this for a possible fix--

http://www.scopestuff.com/ss_ezck.htm

Most problems tend to be mechanical. Have you 'trained' the drive and set the backlash values? Those 2 can have dramatic effects on pointing accuracy. Also, if the optical tube is not in alignment with the mount, then nothing will work correctly. To check that, have the telescope in Alt-Az configuration, inside the house, loosen the RA lock, and shine a laser pointer on the corrector plate. as the telescope is rotated about the RA, the reflected spot should be steady. Adjust the DEC to minimize the diameter of the circle that is drawn. What is left, is the out-of-true on the DEC axis. That can be adjusted with the tube cradle alignment bolts.

My scope sat in a basement for years and when I started it up I got an error the same as you discribe. Through sear luck I found it to be a bad connection where the encoder wire pluged into the battery box.