This is the second LX200 I have had, both have had excellent optics but both have had similar mechanical problems in the drive electronics. Most of the circuits to it are here in the form of Orcad schematic files and the rest copies of print outs in jpg images that can be printed and put together as a circuit. Total download is approx 4 megabytes due to the size of the images. Available also are pictures of how I mounted my Telrad finder and the main pillar mount construction as this scope is permanently polar mounted. The forks are not strong enough when you add extra large weights in the form of 100mm takahashi refractors so there is also a picture of how I strengthened the forks. Since I did this the pointing performance of the scope without additions has improved as well. The orcad schematic Lxopto.sch has the infamous circuit of the optical chopper assembly which with maligned setup causes a lot of the problems that have been experienced by a lot of owners of the scopes in the past. Setup of this circuit is pretty straightforward but the use of an oscilloscope is recommended. My chopper assemblies on both scopes have required setting up at the average user temperature of 15 deg C. This is in the middle of -10degc lowest for me to highest in the summer of 35 deg c.

I have made a series of adapters for scopes they are shown here in this separate page on adapters

The circuits can be downloaded one at a time or complete as a zip file. 1  2  3  4  5  6  7  8  9 The circuit to the header plate where all the connectors go on the front of the scope and the circuit of the hand controller is not available as yet. Ok so what the hell is an Orcad Schematic file, this is a drawing of the circuit done inside a package that is used to design printed circuit boards called Orcad. Many other packages are available but this format is one of the most common and could be read by other packages.

With the forks aluminium plates of 6mm thickness were machined to fit inside the taper of the forks. They were bolted into place with allen head screws in my case they were 2BA thread but mm versions could be used. The same applied to the piece of angle used at the fork base.

The Telrad is mounted on a piece of 16swg aluminium plate cut to 1 inch or so longer than the plastic base holder of the telrad. The normal finder bracket screws were used in the normal finder bracket holes to fix the botton of the plate as shown in the picture. The other curved plate visible in the photograph is used as a base for the mounting plate for the Tak refractor. The mount for that is removable via two hex head bolts. Balancing of the structure is done via the sliding weight rail on the other side of the scope.

(Meade Moan here)
Both scopes from new until adjusted properly at an average working temperature of 15 deg C gave problems with the optical chopper assembly. This is a crude home made bodge made by Meade where they could easily replace it with a proper commercially made unit attached to the motor shaft externally.This would also make the gearbox easier to strip and repair.These devices used to be expensive to buy but now the prices have come down drastically.The device consists of a disc containing 90 slots that allows light from an infra red source diode to pass through to an infra red receiving diode.The light is chopped on and off at 90 times per revolution of the motor shaft by the slits as they traverse the faces of the diode. The slits are narrower than the width of the diode so the light is attenuated following an approximate sinusoidal amplitude modulated curve instead of a a straight extinguishing of the light. The electrical signal from the receiving diodes in this form is them placed on the input of a circuit that changes this sine wave into a square wave ie on  off  at the five volts potential that the computer input ports require. There are two diode sets for this purpose that are offset around the slitted wheel. This makes two signals that are different from each other in time so they are out of phase with each other.If you reverse the motor direction the phase relationship changes again. This can be measured by the computer to find motor shaft direction.One of the signals outputs can be used to measure shaft rotation speed by counting the pulses over time and is used in the closed loop feedback system under computer control of the scope to maintain accurate tracking against a precision quartz crystal timing reference.
If these signals are not set up correctly by the two trimming potentiometers on the circuit board then pulses can be missed causing the scope not to track correctly. There can also be startup problem with the scope in the form of runaway in one direction.The only reliable method that I have found to do this is by using an oscilloscope to look at the sine wave version of these signals before they are squared up and set them for best sine wave shape while slewing the motor at a slow rate with the scope clutches disengaged.These signals come out on three test pins on the small board next to the motor.The only other electrical signal that matters is the worm position detector.This is a magnetic hall effect device. Depending on the strength of a magnetic field at the plastic side of the device the electronic output level from this is set at five volts or zero volts.This sensor is used in the PEC and is tested at startup. If it fails then problems could be caused here. I have never had any problems with this. The sensor output can be checked with a voltmeter and can be seen to be going up and down in voltage by 5 volts when the worm gear is rotating. As this is only once per worm rev the scope has to be revved up to slew rate with the clutches disengaged to see this event. Mechanically the main worm gears definately work better with a touch of Moly slip in the grease and it is advisable to occasionally when possible to re-tension the small springs that pressure the motor plate assembly and the main worms onto the main gears. The only other general mechanical maintenance that I have found useful is to periodically wind the focusser fully out to its stop then fully in to its stop again to re-distribute the lubricant on the focussing assembly. If you look at the picture of the scope the mounting plates may be of interest. They are two 1 inch thick aluminium plates as discs 12 inches in diameter separated by three 30mm allthreads and nuts.The bottom plate is fixed to the concrete mounting pillar. This allows exact levelling of the base of the scope mount by adjustment of the nuts on the all thread.