Fully Populating the Paramount ME Aux 2 (3-line) Serial Pass-Through Port

The Paramount ME has several pass-through ports to facilitate through-the-mount cabling.  These include a 25-pin DB25 (parallel) port, two power ports and two DB9 (serial) ports. While this is a fabulous feature for a robotic telescope mount, the designers chose to populate only 3 lines of one of the DB9 ports while fully populating all 9 lines of the other. Presumably this was done to accommodate the choice of circuit board mounted connectors and cables connecting the Adapter Panel board on the south side of the mount to the Instrument Panel board mounted on the Versa-Plate.  Either a larger interconnecting cable and connectors or an additional cable and connector would have been needed to gain the additional 6 wires to fully populate the Aux 2 Serial port.

As shipped, the Paramount ME’s native Aux 2 Serial port has 3-pins interconnected which correspond to the following RS232 standard lines:

In my system, there are two RoboFocus motors, each with a 9-wire cable connecting the control box mounted on the pier to the motors mounted on the scopes.  The Aux 1 (9-line) Serial port works for one of these connections, but the Aux 2 (3-line) Serial port wiring scheme would not work for the 2nd RoboFocus cable which has 5 active lines to operate the stepper motor.  While the 3-line port would work fine for simple Rx and Tx RS232 communications, I needed to either run the 2nd stepper motor cable though the mount or wire additional pins on the Aux 2 Serial port.  I chose to wire the additional 6 pins which would make this port fully functional for the motor cable and for any future uses that might develop.

To make this modification, remove the 14 socket head cap screws securing the Adapter Panel to the mount.  There is a circuit board on the back of the panel which has 4 cables connected to it.  The cable at the upper right of the board (as viewed from the front of the panel) has very little slack and must be disconnected first to facilitate access to the other 3 cable connectors.  Then disconnect the other three cables, noting the orientation of the cables and connectors.  All of these connectors are different and are keyed so that it is not possible to reconnect them incorrectly though it might be possible to create a problem if inadequate slack was left in the 2 cables which run through the RA and Dec shafts to the Instrument Panel.

It is not necessary to remove the circuit board from the back of the Adapter Panel face plate.  Making sure you don’t mistake the Aux 1 Serial connector for the Aux 2 connector, look closely at the circuit board traces connected to the pins of the Aux 2 Serial connector.  Traces go only to pins 2, 3 and 5 with the other 6 pins not used.  A six wire cable can be soldered to the unused pins, routed through the mount and similarly soldered to the matching pins of the Aux 2 Serial connector on the Instrument Panel circuit board.

Figure 1

Adapter Panel circuit board.
The Aux 2 Serial connector pins and circuit board traces are circled.

The DB9 pin numbers are molded into the outside of the connector but usually require a good light and maybe a magnifier to read them.  To locate pin #1 on the male connector, hold the connector horizontally with the row with the most pins on top (viewed from the outside).  The pins are numbered like you read a book with pin number increasing from left to right.  The upper leftmost pin is #1.  The lower rightmost pin is #9.

Figure 2

The red pins get new wire connections.

Both of the circuit board mounted Paramount connectors are male and correspond to Figure 2.  Mating female connectors have a mirror-image numbering pattern (viewed from the outside). See figure 3.  Connector gender is determined by the nature of the pin (male) or jack (female) connectors internal to the device, not by the nature of the outer shell.

Figure 3

Female DB9 pin numbering.

I used a standard 8 wire unshielded twisted-pair Cat5e cable for the connection with one wire-pair unused.  Standard Cat5 cable has 8 24 gauge stranded wires in 4 pairs.  You can sacrifice an existing Cat5 cable or buy a short spool of raw wire from the local electronics store.  Avoid using solid core wire as it is unreasonably stiff.

Using a low wattage pencil-type soldering iron, carefully add a small amount of solder to the unused pins of the Aux 2 Serial connector which protrude a short distance above the back of the circuit board.  Strip about 1” of the outer insulation off the Cat5 cable to expose the 4 twisted pairs.  Cut one pair off where it exits the outer insulation so there is no chance of it causing a short at some point.  Untwist the remaining 3 pairs of wires from one another and strip about 1/8” of insulation off the 6 wire ends.  Tin these 6 wire ends which can now be soldered to the “open” pins of the serial connector (pins 1, 4 and 6-9).  It doesn’t matter which pins are soldered to which wire so long as the same wire is connected to the identical pin on the Adapter Panel and Instrument Panel circuit boards.

Figure 4

Adapter Panel board with Cat5 cable soldered in place.

Carefully inspect the solder connections with a magnifier to ensure that no solder bridges have developed.  It is also a good idea to use an ohmmeter to check for any shorts between adjacent pins.  Write down which wire color is connected to which pin.  Getting this wrong may cause you all sorts of grief, so double and triple check it.

The free end of the cable can now be routed through the RA shaft, into the Dec housing and out the Dec shaft. Follow the existing wiring, leaving enough slack to accommodate the rotation of the scope axes.  Use a long enough cable to reach the Instrument Panel and cut off the excess when you have run the wire through the mount and can tell where it needs to be cut.  Remount the Adapter Panel to the body of the Paramount after reconnecting the 4 preexisting cables to the circuit board connectors.  It may be a good idea to wire-tie the Cat5 cable to the existing wires before securing the panel in place to prevent repeated wire flexures from mount axis rotation from causing an eventual fatigue failure in the soldered connections.

Figure 5

Replacing the Adapter Panel. The near right connector has a short
cable and must be removed first and reconnected last.

Figure 6

Routing of the Cat5 cable around the declination shaft.

Similar to the Adapter Panel procedure, prepare the “open” pins of the Aux 2 Serial connector on the circuit board mounted on the back of the Instrument Panel as well as the free wire ends.  On this end it is critical to solder the same color wire to a given pin as was done at the other connector.  Double check the wire color and pin number before soldering each of the 6 new connections.  Make sure you don’t mistake the Aux 1 Serial connector for the Aux 2 connector.  Again, inspect your finished soldering for any bridges or cold solder joints.  When done, use an ohmmeter to check continuity across the cable between pins 1 and 1, 2 and 2, etc. and check the pins adjacent to each individual pin for any shorts.  Connect the existing two cables to the circuit board connectors, fit the wires in the Versa-Plate wiring channel, remount the Instrument Panel and you’re good to go with two fully populated DB9 through-the-mount connections.

Figure 7

Instrument Panel with cable soldered to the Aux 2 Serial pins

Should anyone wish to do attempt these modifications, it is at your own risk of course.  No warranty is implied or offered. It is possible to corrupt the integrity of the existing wire connections and not know it or even damage the mount electronics.  Whether or not the Paramount warranty would be honored should something go amiss is an open question.  If this is of concern, consider getting authorization in writing from Software Bisque before proceeding.

Revised 8/18/02