LX200GPS Dec Control board and Motor Replacement                                                     

While preparing the 10" LX200GPS for a up coming out reach event the scope suffered a motor stall error, and would not move in the upward direction. Since I had a previous issue with the Dec drive on this scope, the nasty smell that emanated from the right side fork arm immediately clued me that the problem was either a Dec motor and or Dec controller board issue. 

When I removed the cover I noticed a problem with the Dec controller board and the motor was hot to the touch. So I dug into my spares kit and replaced the Dec board. I tested the scope and while it worked the motor again began to get hot. Not wanting to destroy the newly installed controller board I again raided my spares kit and also replaced the motor.

Removal of the Dec cover shows the grease on the gears is dirty and needs to be replaced. The four connectors on the left (really is toward the bottom of the forks) have to be disconnect they just slide off. The silver knob at the top is removed by loosening up the set screw shown on the bottom left of the knob. The motor assembly will then come out after the 2 hex screws are removed. One of them can be seen at the just over top of the left gear. The other is behind the ty-wraped filter toward the bottom. (Note: the ty-wrap is only on my scope cause I put it there. The last time I replaced the motor.) After the motor assembly is removed the controller board can be taken out, by removing the two Phillips head screws and spring contact.

 		  

The new Dec motor and gear assembly is shown at the top.  This is my last spare motor for the LX200GPS. 

The assembly was delivered from Meade ready to go. Notice the gears are already adjusted. 

Look how clean and shinny  it is. I like shinny things.

 

 

The old controller  board was a Rev C. The new board is a Rev E. This is also my last spare controller board.

 

 

After the old parts were removed the housing was cleaned and the replacement controller board was installed. This image shows the 2 Phillips heads screws (upper right and lower left) that hold the board in place. There is also the spring contact surface for the worm gear that needs to be unscrewed before the controlled board can be remove. It is the silver object with the two small holes just above and to the right of the Phillips screw. The power and control connect has already been attached.

The trunnion is shown here. You will want to be sure it is tight as a loose trunnion will cause the clutch to slip and can do damage. I know first hand as it happened to me. On a normal LX200GPS/R/ACF scope the rod you see above would be attached to the clutch knob and come off when that knob is unscrewed. Because the trunnion on my scope loosened up the threads the hold that rod in were stripped. As a fix I epoxied a longer replacement rod in place and used a custom clutch knob as part of the repair.  The trunnion is tightened by inserting a tool in the two holes. Since I did have a tool I used a hefty Allen key and a rubber hammer.  

The Peterson replacement clutch has become deformed (10'clock position) over the years, from being over tighten. Unfortunately the replacement "Gorilla Knob" makes over tightening of the clutch rather easy to do. But even though the cork clutch material is deformed it still works perfectly. 

The cleaned 5-1/2 inch declination gear is shown back on the trunnion.  The score marks seen on the gear were a result of the clutch slipping when the trunnion loosened up. 

The rest of the trunnion assembly is now installed.  This plate is what caused the  score marks seen in the above image. 

After the trunnion plate the rubber spacer with the metal washer is installed.

Here the fully reassembled Dec drive can be seen (rotated 90 degrees counterclockwise).  The gears still needs to be lubricated and the wires dressed.  The OPT Astro Lock knob was installed before the covers were so the drive assembly could be greased and tested. I refer to the OPT knob as the "Gorilla Knob" I got the name from Pete Peterson who apparently came up with this knob. It is ashamed that OPT doesn't sell it any more. 
During the repair the spring that is used to keep tension on the worm gear assembly was lost.  Lucky for me my local Sears Hardware store sells springs. The one above was purchased for .60 cents and small portion of it was cut off and used as a replacement. 

Dressed and lubed. Its no longer clean and shinny so I might as well put the cover on. 

These are the two damaged chips that caused the latest motor stall. You can clearly see part of the chip on the left exploded and burned. The chip on the right shows signs of excessive heat. The chips will be replace in an attempt to resurrect the board. The motor on the other hand may prove to be more of a problem to repair.  


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