SIGM20: What does the green LED mean?

When the SIGM20 receives a DCC or LocoNet message that affects the signals it controls, the LED flickers off momentarily. This is provided to assist with layout setting up, so that users can tell that a command tot he board has been detected. For example if a signal is controlled by a sensor on a BDL16x board, then when that sensor changes state & puts a message onto LocoNet, the LED will flicker.

If the SIGM20 is powered up, track power is on and the green LED isn't on, it points to a problem in cabling between the SIGM20 and the command station. The following suggestions are offered:

  • Check that the SIGM20 has power properly applied.
  • Is the board correctly powered? SIGM20 boards should not share a transformer winding with the boosters, or with power fed to some other types of device e.g. DS54 or DAC10. This can lead to "ground loops" with short circuits introduced via the return path. There is more advice in the general FAQ.
  • Check that track power really is on.
  • Check that jumper JP1 is removed.
  • Check that the SIGM20 cable isn't connected into the front of a utility panel, e.g. UP3.
  • Check the integrity of the LocoNet cables between the SIGM20 and command station. Sometimes the connectors don't crimp properly, leaving a high resistance connection. An LT1 type tester doesn't always detect this!