SoundTraxx LC series decoders

The familiar yellow shrink wrapped decoder from SoundTraxx. See historical information in the column at the right.


Connections on the DSD-AT100LC board

Especially when attaching LEDs, it is really helpful to know what the polarity is if the lighting terminals on this decoder. This photo shows the NMRA standard color code by pin for the decoder. The two magenta squares represent the speaker terminals - polarity is immaterial unless you are using multiple speakers.

820040 820041 820042 820043 820044

Connections on the DSD-LL110LC board

Some folks choose to hard wire this board to their locos. Here is a quick reference to the NMRA standard colors for this board. The two magenta squares represent the speaker terminals - polarity is immaterial unless you are using multiple speakers.


Using LEDs with the LC series decoders

SoundTraxx says that the LC series decoders are not recommended for use with LEDs. Here's why. The design of the decoder has a small amount of current being routed to the lighting circuits during the generation of certain sounds. If incandescent bulbs are used, these pulses of current are not enough to illuminate the bulbs. However, LEDs respond very rapidly and will show a small glow from time to time. There is nothing about this that is incorrect, just a bit less than totally esthetic.

There are two ways to deal with this:

1) Live with it - many folks don't even notice or

2) Fix it - add a resistor and capacitor in parallel with the LED as shown in the drawing below (the magenta colored components). While the drawing below shows the DSD-AT100LC board (the most cryptic as to colors), the basic connection is the same for all LC series decoders, just follow the color code! In this drawing, the component values are a bit hard to read. The resistors are all 1000 (1K) ohms 1/8 watt and the capacitors are 0.1 uF at any voltage larger than 10 volts - Litchfield Station stocks 50 volt versions.


Adding "Keep Alive" capacitors

Many folks want to eliminate or reduce the drop out of sound created by interrupted connections to their DSD decoders. Any of these modifications will eliminate any warranty from SoundTraxx. If you want to do this there is data on the web. A friend of Mr. DCC has comprehensive data on this. CLICK HERE

Using them as a sound-only decoder

Many folks decide to use older decoders for their sound generating capabilities and, perhaps lighting effects. Here are some suggestions:

  • Programming - since the LC series doesn't support decoder locking, you need to provide a way to physically separate the two decoders (with a plug and socket) so you can talk to one decoder or the other.
  • Motor - If you put a 100 ohm 1/2 watt resistor between the gray and orange motor wires or contacts on the DSD, you can then get acknowledgments back when you program.
  • If you set the DSD for Speed Table operation with the USER SPEED TABLE selected and set all speed steps to zero, then you won't be using your DCC power to heat up the resistor when you are running!
  • To do this, read CV 29 and add 16 to that value and write the result back into CV 29. Then set CV25 = 16 and set all the CVs from CV 68 through CV 94 to a value of zero.
Copyright © Bruce F. Petrarca 2007 - 2017; All Rights Reserved