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LX200 Classic tracks backwards when hand controller is plugged in

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#1 Paul Sweeney

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Posted 07 January 2020 - 08:57 AM

Hi all,

 

Here is a problem that maybe somebody has already solved: The LX200 Classic runs correctly without the hand controller. But plug in the hand controller, and it tracks backwards. It is not the North/South switch. It is an older LX200, from the 90's. Spare parts ( a new hand controller) are no longer available. I'm baffled. Anybody have any idea what could be wrong and how it can be fixed?



#2 Jim Davis

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Posted 07 January 2020 - 10:08 AM

First, do you have the control panel on the mount facing North? Second, how are you controlling the scope without the hand controller? Are you performing an alignment?



#3 DAVIDG

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Posted 07 January 2020 - 01:14 PM

 Looking at the schematic from here  http://www.lx200classic.com/

 

 the North/.South switch is the only connection that should control the direction of the motor. When it is  the North position the I/O line should be pulled high to +5 volts and when in the South position it is pulled Low to ground.

    The hand controller sends commands back to the main board. If the I/O line for the North/South switch has the correct voltage on it and since your  in Germany that would be pulled high +5 volt, then the only thing that comes to mind is the button on the hand controller to cause the scope to slew in the opposite direction is stuck in the On position.  To test this you would need to open the hand controller and unplug the ribbon cable from the keypad.  

  If the keypad is bad you still  might be able can get replacement keypads from  Ron Sampson http://www.imjeffp.com/handcontroller/

 

             - Dave 


Edited by DAVIDG, 07 January 2020 - 03:06 PM.


#4 Paul Sweeney

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Posted 08 January 2020 - 11:31 AM

Hi guys,

Thanks for the input!

The scope was bought new in about 1993 and has been on a permanent pier in an observatory, and has worked fine all these years. A short time before this problem started, my friend accidently bumped the north/south switch, so there was where we started our troubleshooting. Without the controller, the motors run in the right direction. Hit the N/S switch, and they run reverse direction. So no problem there. Then we cleaned and inspected the contacts for the hand controller. They are in good shape, so no problem there. So we figured that we either an electrical or mechanical problem with the hand controller. But before we opened that up, I wanted to ask for advice. Thanks again for the help!

 

Paul



#5 DAVIDG

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Posted 08 January 2020 - 01:20 PM

 Here is another test to try. Put the N/S switch in the direction that makes the motors run in reverse and with the hand controller plugged in see if  it  still keep going in reverse ? If so then that points to the hand controller send the command to drive  the scope in reverse  On the hand controller there is a capacitor right under the ribbon cable for the keypad. This capacitor is known to burn up and damage the ribbon cable. It is possible that this has happened causing the problem your seeing.

 

                           - Dave 



#6 rferrante

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Posted 09 January 2020 - 04:58 PM

Paul is this a Revision 3.xx scope? If so, I don't believe the hand controller knows which way the N/S switch is set. It does not send tracking information to the telescope either, so I don't feel it could be sending erroneous information that would cause the scope to change direction.

 

In the period before you start pressing keys on the hand controller's keypad, it sends no information to the telescope other than its 4-byte "wake up" message, which is always the same. Before the wake up message, the scope sends no information to the hand controller, so the hand controller could not know about the N/S switch before sending its only message to the scope (which is always the same anyway).

 

After the wake up message, some data comes from the telescope to the hand controller, but if you have not pressed any keys, the hand controller has sent nothing back the other way. Also, the data sent by the telescope at that time is identical whichever way the N/S switch is set, so the hand controller is ignorant of that setting.

 

Again, this is all for a revision 3 scope only.

 

--Rob



#7 Paul Sweeney

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Posted 16 January 2020 - 05:35 AM

Hi all,

 

We opened up the hand controller, and discovered a tiny nut and bolt between the key and the internal contact, which was continually "pressing" the key and causing it to go backwards. We couldn't find a place in the hand controller where it might have come from, so it must have been accidentally left in there at the factory, and just sitting in the controller all these years. I'm really glad that it turned out to be such a simple problem to solve. Thanks again for the input!

 

Paul


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#8 AstroChampion

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Posted 19 January 2020 - 10:19 AM

Wow, lucky it didn’t cause a serious problem by being a jumper somewhere.


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