LX200GPS Focus Jack Modification

The Meade #1209 Zero Image Shift Microfocuser is provided with all LX200GPS telescopes and is an option for others.  With the LX200GPS, it is connected to the base using a coiled cable, and this cable often gets caught up as the scope is rotated.  The modification described here provides a second jack for the microfocuser on the inside of the left arm, thus eliminating the tangled wire issue.

This modification requires soldering small wires in a tight location; do not attempt it if you are not comfortable with this task (see pictures below).  The modification also requires removal of the internal battery holders and associated wires; this means of power is seldom used (I have never used it).

The first step is to remove the center cover plate, both battery holders and the battery compartment in the left fork. IMG_9899.jpg (21011 bytes)
The wires from the battery holders are red and black; the two holders are in series (#1 in the picture) to provide 12 volts.  The red wire from the left holder (#2) and the black wire from the right arm (#3) go down to the base through the black tubing in the center.

Cut the wires at the battery holders and pull them out of the arms.  Wire #1 will be free, and the other two will still go through the tubing to the base.

IMG_9900.jpg (16507 bytes)
In the base, these wires come out of the tubing (1) and terminate at the blue plug on the board (2). IMG_0005.jpg (27448 bytes)
Pull this blue plug off the pins on the board.  It will be discarded when the power wires are pulled out of the tubing (not yet!! - see below). IMG_0012.jpg (27427 bytes)
Now pull only one of the power wires out of the tubing leaving the other one as a pull wire.  Solder the top of the remaining wire to a piece of ribbon wire (3 wires) as shown.  The wire I had was about #26; three separate wires would also work fine. IMG_0016.jpg (8522 bytes)
Using this pull wire, pull the ribbon wire through the tubing.   It should not be necessary to remove the cable tie on the top as the ribbon wire should be about the size of the two power wires. IMG_0017.jpg (22920 bytes)
Pull the ribbon wire through the tubing and run it through the existing tie wrap.

To make it easier to feed the other end into the battery compartment, remove the plastic plate on the bottom of the left arm and route the wire as shown (2).

IMG_0018.jpg (27287 bytes)
The ribbon wire should now run from the left arm battery compartment through the tubing and down to the base. IMG_0023.jpg (20822 bytes)
Identify the back of the focus power jack as shown here (1,2,3).   The TIP of the connector is at 3, the SLEEVE is at 2, and the shell or common is at 1. IMG_0010.jpg (21368 bytes)
On the ribbon wire, strip the insulation and tin the ends; this should be < 1/8". IMG_0020.jpg (15896 bytes)
Carefully tack solder these wires to the circuit board pads as shown.  There is another trace close to the "sleeve" connection (on the "tip" connection side).  Use care not to damage or solder to it. IMG_0022.jpg (29802 bytes)
A 1/8" three connector jack was mounted on the plastic battery door as shown and wired up to be identical to the original focuser jack.  Note that all of the LX200 circuit is floating above ground, so do not mount the jack on the metal arm. IMG_0024.jpg (18868 bytes)
I mounted the plug toward the back as shown.  I used a jack I had "in stock" which was not designed for the thickness of the plastic door (Radio Shack #274-246), so I had to counter-sink the nut.  Jacks for thicker panels may be available and would have made this job somewhat easier. IMG_0026.jpg (12677 bytes)
In use, the focuser plugs in as shown. IMG_0029.jpg (18257 bytes)
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