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LX200 Refurbishment


COMPLETE MECH / ELEC REPLACEMENT
We have had a few customers wishing to repair their telescopes, but wanting to go a different route to the Meade Repair Kit. We have applied various strategies with different upgrades but we are now happy that the presentation here is the way to go. The result is a mechanically beefed up telescope fitted with GOTO electronics of equivalent performance to the LX200 Classic telescopes. See this link for the LX200 Upgrade kit that is now available from us. It is now QUIET and has a much IMPROVED GEARBOX.

GENERAL ADVICE
The Meade castings are fairly soft and so they are easy to machine with hand tools. There are six holes to drill to fix on the new brackets and some are to be tapped. The AWR metalwork has adjustments to cope with slightly inaccurate drilling but good tolerances are generally required. Do not over tighten bolts going back into the Meade castings as you can strip the thread. This is not a disaster, as the holes can be drilled out and re-tapped. AWR can do the machining on the brackets if required, or even doing the whole job but the telescope will have to be shipped to us.

DO NOT LOSE THE SPRINGS when you take the slow motion brackets off the telescope! They will ping off. If they do need replacement you need a working pressure about 1 to 1.5kg when the brackets are adjusted. This moving component is retained to minimise backlash in the final assemblies.

STRIP DOWN
We need to get right down to the slow motion axis. Both RA and DEC brackets are treated the same.

DEC AXIS
It is suggested you do a dry run to check the location of the parts to see what needs to be done at various stages during the rebuild.The new DEC motor fits outside on the fork strut. This has quite an angle on it and so we need to fix a plate on very securely to the fork to provide a flat surface for the motor to mount onto. The motor shaft must end up exactly parallel to the slow motion shaft so some adjustment by shims may be required to tilt the fork plate.

The fork plate mounting has 2 countersunk M4 screws with clearance holes in the fork casting and nuts / washers on the other side. The other two mounting bolts are M4 and must go into tapped holes as there is insufficient space inside the casting to use nuts.

The other problem we have is that if the gears are pushed home on the shafts, the teeth will not meet. To achieve proper mesh of the gear teeth, both gears are overhanging the end of the shafts by about 6mm. This is not a problem as the gears are rugged chunky components. The other adjustment that we did is to elongate the Meade bracket plate to allow it to slide closer to the motor by 2mm.

The new 58 tooth gear on the slow motion shaft has plenty of clearance on this axis (it is just under 30mm diameter). It has a grub screw to secure but, belt and braces, we also used superglue.

The motor is already mounted on a flange with 4 securing holes (elongated) to allow adjustment of the mesh with the 58 tooth gear on the slow motion axis. The motor mounting cable needs a slot cut in the Meade cover plate and it is placed along the track of the original motor cable to the RJ45 coupler at the base of the fork. Plug in the Meade coiled DEC cable from the fork to the new base plate and then power up the DEC axis using the microstep drivebox. Check it is all functioning before the cover plate over the DEC slow motion assembly is replaced.

New DEC Components

Brackets in place

Finished Assembly

RA AXIS
The RA axis rebuild is a little more intricate. The motor bracket is a plate with an idler gear wheel on a stud which is to be bolted onto the end of the Meade hinged slow motion bracket. We are after a solid motor fixed in position but allowing the original sprung loaded slow motion axis still to function. By keeping the second gear in line with the hinge axis there is very little backlash introduced in the gear train when the slow motion axis moves in or out. The modified RA hinged slow motion axis is shown in the picture with two M4 bolts in the end ready to take the vertical motor plate. The small pcb also needs to be spaced away by 10mm to allow space for the motor body.

The hinged bracket mounting needs attention. The elongated holes must be adjusted so there is enough space for the 58 tooth gear to rotate without fouling the vertical part of the casting. About 0.5mm of clearance is required and you get this by angling the bracket so it is not parallel to the backface of the base casting. Then the vertical plate needs fitting. Offer it up to the bracket and mark the two mounting holes. Make sure there is clearance between the bolt head and the 58 tooth gear. These two holes must then be drilled and tapped to take M4 bolts. The motor mounting plate can then be added and fixed in place. The hinged part should still work without binding, it may be necessary to add a shim to space the motor mounting plate away. The complete motor bracket and mounting plate is then fixed back on the scope. Check the rotation of the gears to make sure there is no binding.

Finally the motor is added on to the bracket. There should be a tiny bit of backlash in this adjustment. Do the bolts up tight as there is enough power from the motor to force it out of adjustment if there is any binding. Then power up the motor and check it rotates properly.

Modifid RA Bracket

Motor Mounting Plate

Motor Mounted

FINISHING OFF
Check the tightness and adjustment of the gears. Power up each axis in turn and check that the motors operate smoothly without binding. A slew rate of up to 2.4 degrees per second should be achieved. Fit the front connector plate and plug in the internal motor cable to the RA motor. Plug in the internal cable to the 8 way socket for the periodic error to function. Everything should now be done.

The motor cabling to the drivebox is identical on each axis. The gear ratio is also the same on both axes. This makes an easy job of fault finding as bits can be swapped.

Comments to Alan Buckman at AWR Technology.


November 2006 AWR Technology HOME PAGE www.awrtech.co.uk