Hi all, I've been a bit busy performing an upgrade to the pre 2012 Nexstar GT mount I have had for a number of years. As everyone knows, you can not use the Nexstar+ hand control with the unit as it is. However, you can change out the motor control board to a NXW435, do a little wiring modification to the hand control /power plug board wiring, and remove the wires from the MC board plug, and replace them in the correct order, and it will now be able to use the Nexstar+ hand control. I just finished figuring out the wiring changes and installing a board I got from a member here on CN. (Thanks George).
I did this mod to my own mount. If you attempt this mod using this write up, you do so at your own risk. This write up was just to show what I did to modify my mount.
My mount was working fine, but I was limited to using the non + HC, and was limited to firmware 4.04, and there haven't been any updates for it in a number of years. The old board/HC combination also would not work with the Celestron GPS module or the SkyPortal WIFI unit. I happen to recently come across a post 2012 GT mount and discovered it would work with both accessories. The older GT and later GT also will not work with the current version of CPWI. My LST mount will, but not the GT's. I can live with that.
Another plus with this mod, is you can now use Celestron Firmware Manager (CFW) to update the Hand Control firmware to the latest (5.31.9200).
I do not know if there will be any future later GT MC board updates (I doubt it), but you can take advantage of future HC firmware updates.
So with that all said, here is a quick walk through on how to do the upgrade.
First get a NXW435 Motor Control board (MC board).
Then remove the two screws holding the plastic cover on the mount.
Unplug the hand control wire from the MC board.
Separate the two pieces and set the mount portion that holds the MC board to the side. We are going to work with the Hand Control plug/power board.
On the outside of the unit, you will see the power plug. Using a 3/8 nut driver (its probably metric, but the 3/8 works) remove the nut that holds the power plug to the plastic case. set nut and lock washer aside.
Flip the plastic cover over and remove the three screws that hold the board to the plastic case. remove the board from the case. Set the plastic case aside.
now looking at the wiring soldered to the circuit board. Find the yellow wire, and clip it flush with the board surface. This wire will not be used again. DO NOT cut it at the plug.
using a soldering iron, and a short piece of wire, jumper across solder pads 2 and 4. One later GT plug board, that is the only difference between the early and late boards. On th elate board, there is no connection between the two solder pads. ON the late GT board, there is a short trace connecting the two pads.
The mod to the plug board is complete.
Now on the end of the wiring harness from the plug board, there is a 6pin plug with a wire in all 6 locations. with a marker, mark the location where the white wire is inserted. Carefully remove all the wires with attached plugs from the plug body. I made a tool from a small paperclip that I flattened one end to serve as a pin removal tool. You can also carefully lift the plastic tabs (just a tiny bit, do not break them) and remove the wires. Now starting on the end of the board where the white wire was inserted. move over one slot and insert the wires in the following order.
plug board wire color pin header
1 N/C No wire-- This is the slot you marked with the marker.
1 White wire 2
2 Blue wire 4
3 Red wire 3
5 Black wire 5
6 Brown wire 6
4 Yellow wire Not used
You will have the yellow wire left over. You may dispose of it.
That's it, the modifications to the plug board are complete. Reinstall the same way you removed it from the plastic housing.
Now onto the MC board.
Remove the two motor wire plugs form the MC board. Note the orientation of the existing board. The new MC board will be installed in the same orientation. With the plugs in the same locations.
Remove the two screws, remove the old board, place the new board, and reinstall the screws. Reattach the motor wires to the board. Making sure you get the Alt motor connected to the Alt socket on the MC board, and the AZ plug to the matching AZ socket. Plug the HC plug board to the socket marked as AUX. check everything over closely to make sure you have everything connected correctly (especially the wires to the AUX socket). Replace the cover. You can install the cover screws now, or wait until you test it.
Plug a Nexstar+ hand control into it socket on the mount, then apply power. The hand control will display Initializing, then it will give directions to start the alignment.
At this [point, I press the menu button and scroll through until you get to utility then hit enter. Scroll through the utility menu until you get to version, then press enter. The display will now show the HC firmware (in my case 5.31.9200, and the motor control firmware which should be 5.21.
Pat yourself on the back, you now have a post 2012 Nexstar+ GT.
Disclaimer: I did this mod to my own mount. If you attempt this mod using this write up, you do so at your own risk. This write up was just to show what I did to modify my mount.
Here are a couple of pictures that show the similarities between the MC boards and the HC plug boards.
This picture shows the one difference between the two plug boards
This picture is of the original MC board and the NXW435 MC board
This picture is of the modified old plug board with pads 2 and 4 jumpered and installed back in the mount.
Edited by MitchK, 12 February 2020 - 10:48 AM.