FAQ:How to Revive a Dead Decoder

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A locomotive with a DCC Multifunction Decoder refuses to respond to commands from the throttle?

For most of these steps, DecoderPro can be of great assistance. The software can identify the decoder, read various CVs, and offers easy methods to force a reset if needed.

Before starting, read the manual for the locomotive and decoder, to understand which functions it may use for startup, brake and mute.
  1. If the locomotive moves, yet no sound, the mute function may be active. Disable the mute and it should make noise
  2. If it makes noise, responds to function commands but will not move, a Brake function may be active.
    1. It is possible the speed table may be incorrectly set.
  3. The decoder may have a startup/shutdown procedure. Press the appropriate function key to initiate the startup. Like the prototype, they won't move when the engine is not running.
  4. If the lights come on, that is a sign the decoder is working. The issue is likely related to addressing.
  5. Attempt to address the locomotive using the number on its cab. Most modellers follow this convention. If not, use the convention you use.
    1. With an NCE system, should that not work, add a leading zero, as the locomotive may be using an extended address which is equivalent to a Primary address (1–127).
  6. Try the default address. Numerous voices on the internet assert it is 3, which while true, is not necessarily true. The manufacturer is permitted to use any valid address when the vehicle ships with a decoder. If in doubt, check the manuals that came with the locomotive.
  7. Write a value of 0 (zero) to CV19. It is possible the locomotive was part of a consist, and CV19 will override any preferences regarding Primary or Extended Addresses.

On occasion, a short circuit or unexpected variations in track power scrambles the decoder's programming or its checksum. The decoder, upon restarting and without exception, verifies the content of its memory against the checksum. If the verification fails, the decoder resets to its default values.

Note the expression "factory default" was not applied. Some decoders, such as ESU's manufactures, permit the user to dictate a number of defaults, including a default address.

If the decoder is a retail decoder (purchased from a hobby shop and installed) then the default address is definitely "3". Exception: Manufactures from ESU must be programmed at the point of sale, which loads the firmware and sound project. The default address can any valid address, as well as a number of other parameters, set to whatever the customer desires.

If these steps fail, attempt a reset. This is normally executed by writing a specified value to CV8. First, read CV8 to determine the manufacturer of the decoder, then use the appropriate values to initiate a reset.

The reset must be done on a programming track, as Service Mode is required. Service Mode uses a broadcast protocol, so it is unnecessary to know the address of the decoder in question. Operations Mode[1] could be used, but it requires use of address "0", which initiates a broadcast write. As the name implies, it alters each and every decoder on the layout.

Caution: A decoder reset ends in all decoder customisations being lost. Some decoders have options for a reset, but for many it is a return to preset defaults.

  1. Operations Mode writes to a specified decoder address in normal usage, while it can use a broadcast protocol when address 0 is specified.