LX90 (non GPS). The DEC is always pointing almost 4 degrees out. This was the result on a RA 180 degree DEC 80 degree test, The RA is spot on 180’ but the DEC is almost 4 degrees out each time. On the first motor stop, the DEC is spot on the 80', when the RA has completed is run the DEC will then creep on another almost 4'. I have found that on a LX90 that is working correctly that the RA stops almost 4' short of 180 and the DEC stops almost 4'short of 80'. then both drives will creep up to the correct settings 180' and 80'.
I have done a flash reload of the firmware, changed the handset for a known correctly working one and changed the motor set. The problem is still there. I suspect that the driver card is faulty but cannot obtain one in the UK.
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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.
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.
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?
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.