"How to" Series

Installing and testing a decoder: Steps 18 - 24


Lenz Silver MP (0.91"L x 0.66"Wx 0.12"H)


Step 18 - Choose a decoder that will fit within the confines of the cab.


Step 19 - Snip or unsolder the green, brown, and violet wires and NRMA plug, if any, as these will not be needed.


NOTE: Ultimately, the decoder choice for your SW1 is really up to you.  I chose the Lenz Silver MP (HO).  Other recommen-dations have been the TCS M1, NCE N12SR, and Digitrax DZ143.


Even though a smaller decoder would have probably made installation easier and faster, I have no regrets with chosing the Lenz Silver MP.  I've been VERY happy with the low-speed switching of both the Gold- and Silver-series decoders.  And this one is no exception. Speed step 001 yielded a mind-numbing 0.33 sMHP.  (And that was without me even tweaking anything!)

Making room for decoder in cab area


Step 20 - Remove the plastic cab wheel bracket and column from cab frame.  (They should twist off very easily.)  This will allow needed room for the Lenz decoder.  If using a smaller decoder, you can just leave these in place.


NOTE: Upgraded rear U-joint visible in pictures at left is installed incorrectly.  Do NOT use it as a reference!

Mounting the decoder


Step 21 - Cut two (2) strips of 1/8 x 5/8" double-stick foam tape and center them on the inward sill above of the frame, above the rear drive train.


Step 22 - Mount the decoder to the double-stick foam tape.  Be sure to butt the wire side edge of the decoder to the side frame of the cab area and align the back edge to the back edge of the frame.  This is important so that the decoder does not interfere with the cab properly seating onto the frame during assembly.


HELPFUL TIP: Unsolder and rotate each decoder wire 180 degrees on its soldering pad so that they pointed toward the center of the cab rather than away from the cab.  This eases the transition of the wires from the decoder once the cab was installed.  If you choose to do this:


  1. Draw a wiring diagram so you know which wire goes to which pad on the decoder

  2. Read **REMINDER at the bottom of the page to save yourself an extra step.


Step 23 - Solder all decoder wires to their corresponding wires and/or soldering pads:


Wiring diagram


















*1K resistor must be soldered to lead "in series"

**This can run from the light board pad to the Anode lead


NOTE: Since there is minimal clearance above the light board once the hood is in place, resistors should be isolated to the cab space, above the decoder.

Testing the decoder


Step 24 - With everything wired up and before reassembly, it's time to test the decoder.  Place the SW1 on your programming track* and operate it on address "3" with your DCC system.  Check it in forward and reverse to see if your LEDs are working properly. Correct any issues/problems** before proceeding.


*CAUTION: It's VERY important that you test your decoder installation on the programming track rather than your main line.  If, by chance, you've inadvertantly wired something incorrectly, you greatly reduce the chances of frying your decoder by operating it on your programming track.


**REMINDER: As mentioned in HELPFUL TIP under Step 6, your SW1 will run backwards in forward because the motor is in upside down.  If you haven't already swapped the motor wires previously so that the gray wire is on the bottom motor contact and the orange wire on the top contact, all you need to do is to swap them on the decoder.  Problem solved!  The 2nd decoder picture above shows you the wires in the corrected orientation.