Command 2000 Modification





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Add connectors for two more walkaround throttles to your MRC Command 2000.

As explained in the introduction, I needed two more throttles to control switchers in two yards some distance from my command station.  Tearing the slide controls and push buttons out of the command station and moving them to appropriate places would do the job.  But it would also ruin the resale value of the unit, and it would no longer be possible to use it to control my portable large scale layout.  So another approach was taken.  Four 1/8" stereo phone jacks were added to the back of the command station, one each for throttle 2 speed control, throttle 2 direction control, throttle 3 speed control and throttle 3 direction control.  Plugging in an external speed control automatically disconnects the appropriate speed control on the command station while plugging in an external direction control  leaves the direction control on the command station active.  This scheme prevents the speed controls on the command station from accidentally interfering with the remote speed controls, but leaves the push buttons available for programming.

WARNING: This is not a good project unless you are truly proficient in the art of soldering or have a friend who is.  The Command 2000 can easily be damaged by a botched soldering job and MRC will not cover that under warrantee.

Basic Approach

  The photo shows the four miniature stereo phone jacks on the back of the command station case (just below the label showing their functions.)

Because the speed controls built into the command station were not designed to be disconnected, they do not have any memory function.  This means that any speed controls you add cannot be unplugged from remotely located jacks and still have the trains continue at the same speed, as happens with the normal walkarounds.  However, they can be equipped with extra wire to let them operate as tethered walkarounds, which for yard switcher service, is ideal.

Opening the Case

Opening the case may be the hardest part of the whole operation.  Unfortunately, MRC has the habit of using strange screws in their cases, such as the Torx Tamper Proof screw shown at left, enlarged about 8x.  These screws cannot be removed with a regular Torx screw driver because they have a pin in the centre of the slot which keeps a regular Torx screw driver out.  Attempting to drill these hardened screws out is a sure-fire way of melting the surrounding plastic and ruining the case. 
What is required is a T-10 Torx Tamper Proof screwdriver with a 1/4" or smaller shaft diameter.  The business end of such a screwdriver is shown at left, enlarged about 16x.  The hole in the centre slips over the centre pin in the screw head and allows the flutes to engage.  The diameter of the shaft is limited by the access holes in the bottom of the command station case.  Drilling the centre out of a regular Torx screw driver is not an option unless you have access to tiny tungsten carbide or diamond drills.  With the proper screw driver, the six screws are easily removed from the bottom of the case.  The two halves of the case can then be separated.

When the bottom is removed, all the works are found in the top half of the case.  In this and subsequent  photos, the case is shown with the terminal strip at the top.  The secret of the two extra screw terminals in the middle of the strip is laid bare - one terminal has no connection, the other has a brown "mystery wire" going to the circuit board.  Speaking of the circuit board, it is firmly bolted to a large aluminum sheet which forms the heat sink for the output transistors.  DO NOT remove the four bolts holding the circuit board and heat sink together.  Rather, remove the four screws indicated by arrows, then gently lift the circuit board and heat sink, being careful not to strain the wires below.

Modifying the Wiring


If you are an electronics boffin, then the schematic diagram above may be all you need to make the necessary alterations to your Command 2000.  For building the remote throttles, you also need to know that the push buttons are bounce free membrane types and the  pots are 10k, either linear or log taper, your choice.  If electronics is not your cup of tea, read on.

With the circuit board and heat sink tilted up, the slide type speed controls can be seen underneath.  This is where our wiring modifications start.  On the right is speed control #1 with two red wires, one to each of the bottom terminals (the colours are those I found in my unit - yours may be different.)  The connections of speed control #1 are left undisturbed.  The other two speed controls have a common black wire that connects one terminal of each control to point L1 on the circuit board. Start modifying the wiring by connecting another black wire to the existing one by soldering it to the terminal of speed control #2.  (I used fine, stranded wire stripped out of a piece of flexible, flat telephone cable.  The six wire type has red, green, yellow, black, blue and white  insulated wires which allows you to follow the colour coding used here.)   Run the added black wire to the back of the case and connect it to the "ring" terminal of each speed control jack.  (See the diagram below for jack connections.)  The second terminal on speed control #2 originally connects to L3 via a yellow wire.  Unsolder  the yellow wire from speed control #2 and extend it by soldering a new length of yellow wire to the free end of the old one, and cover the joint with shrink tubing.  Then connect the other end to the "tip" terminal of the #2 speed jack.  Finally, I complete the rewiring of the #2 speed control by connecting a white wire to the terminal from which you unsoldered the yellow wire, and connect its other end to the "tip switch" contact of the #2 speed jack.  Similarly, disconnect the green wire from speed control #3, extend it and connect it to the "tip" terminal of the #3 speed jack.  Then use a length of blue wire to connect the freed up terminal of speed control #3 to the "tip switch" contact of speed jack #3 


Above is a semi schematic diagram of typical stereo phone jacks.  The layout of the terminal lugs may be different, but their internal connections are usually indicated somewhere, either printed on a card, moulded into the side of the jack, or best of all, visible through a clear plastic side on the jack body.  In these diagrams, arrow heads represent switch contacts.  The switches in the upper diagram are in their normally closed position.  This means any signal present at the "tip switch" terminal will appear at the "tip" terminal.  In the lower diagram, the switches are forced open by a stereo phone plug.  Any signal at the "tip switch" terminal is interrupted, but any signal present at the tip of the phone plug appears at the "tip" terminal.  The "ring" and "ring switch" work the same way.  There is a third terminal which in stereo headphones for example is common to both the ring circuit and the tip circuit.  We do not use the common connections in this project because they are connected to the exposed nuts which could be easily shorted which would damage the internal circuits of the command station.

The black,  yellow, white, green and blue wires to the speed jacks are bundled together near the centre of the photo while the black, green, red and yellow wires to the direction jacks curve out of the photo to the right.  The four red arrows at the top of the photo indicate the four jacks.  The four red arrows near the centre of the photo point to four of the six latches that hold the push button assembly into the case.

Continue modifying the wiring by adding wires to the #2 and #3 push buttons.  First remove the push button assembly by gently pressing the latches sideways to unlock them while simultaneously pressing the assembly out of the case.  In the photo, the removed assembly is sitting upside down on top of the case.

Add four wires to the solder dots indicated by the red arrows.  This can be a bit tricky, but here is a way that works.  Strip the wires, flux them with liquid rosin, and tin them with solder.  This will cause melt back of the insulation, exposing more wire, but the flux will normally assure that they are tinned right up to the end of the insulation.  Clip off all but 1/16" (1 mm) of the tinned wire.  Then flux one wire and the corresponding solder dot.  Place the wire on the dot and touch briefly with the soldering iron.  This should give you a solid joint with no further melt back of the insulation.  Repeat for the other three wires.  In the photo, the wires from left to right are green, black, yellow and red.

Connect the other ends of the wires to the direction jacks.  The black and green go to the ring and tip of the #2 direction jack and the red and yellow go to the ring and tip of the #3 direction jack.


Modifying MRC Walkarounds  An easy modification of your MRC Command 2000 Walkaround throttles will allow them to be used in pairs without interfering with one another

Building Tethered Walkarounds   Use two of these with your modified command station to move throttles two and three elsewhere on your layout.  Optional extended low speed control is ideal for switching.

Building Memory Walkarounds  Use two of these with your command station, modified or not, to replace the memory walkarounds supplied by MRC.

Cords and Cables  Some guidance on extension cords and installing throttle stations. 

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this page was created 4 April 2000, last modified 28 February 2001