How To Expert Tips 10 (or 11) ways to blow up a decoder

10 (or 11) ways to blow up a decoder

By Larry Puckett | February 1, 2023

It’s important to know what NOT to do while installing a decoder

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A locomotive shell with multiple colors of wires coming from a decoder

How do you blow up a decoder?

A collection of compact DCC sound decoders on a white background

  1. Fail to isolate the motor, creating a dead short.
    Various older locomotives used the chassis as part of the power pathway to one of the motor brushes, making the chassis is electrically live. This can be easily fixed with insulating tape placed under the motor and plastic or nylon mounting screws. This is only one way to blow up a decoder.

    The frame of a locomotive with blue tape on the bottom and motor next to the frame
    To isolate the motor, Larry first needed to apply a layer of vinyl electrical tape to the motor-mount area on the chassis. Larry Puckett photo
  2. Install the decoder without testing the stall current (or checking it in a MR review) and using a decoder with too low of an amperage rating.
    Older motors, especially open frame three pole types, may draw in excess of one amp of current. These require a decoder capable of supplying that amount of current or the components may be damaged. Better yet install a modern replacement motor.
  3. Install a new decoder and place the locomotive directly on the main track before testing the installation on the programming track.
    Programming track current is limited to 250 milliamps to prevent damage to a decoder in case of a short.
  4. Install a decoder in an older locomotive without giving it a complete overhaul, especially when coming out of storage.
    Old locomotives left sitting in a box may run poorly and draw excessive current which can damage a decoder. Gear lube in particular may harden over time and prevent the motor from turning creating an excessive current demand.
  5. Drop a free or exposed wire on the rails or live chassis while giving the installation a “quick” test.
    Unfortunately modelers are all too often in such a hurry to test a new decoder that they will immediately place it on the track to see how it runs even before protecting solder joints and exposed wires. One split second of inattention can blow up a decoder.
  6. Use cellophane or black electrical tape instead of heat shrink tubing to insulate wire solder joints or fail to insulate them at all.
    Cellophane and electrical tape are not designed for these types of installations and will soften and fall off soon after installation, resulting in the potential for a short circuit. Use heat shrink tubing instead.
  7. Fail to use couplers with insulated shanks on locomotives that use the chassis as part of the electrical path and have body-mounted coupler boxes.
    Older locomotives such as those made by Athearn, Atlas, and LifeLike used the chassis as part of the electrical pathway. If a metal coupler is installed in a draft gear box cast into the chassis, it can result in a short between locomotives and potentially damage decoders.
  8. Set the volume too high and overdrive the onboard audio amplifier.
    When either the incorrect speaker is installed or is not installed properly it may provide inadequate volume and modelers may increase the volume setting to compensate. If set too high for the speaker, the audio components on the decoder may fail.
  9. Install a four-ohm speaker with a decoder rated for eight ohms.
    Most decoders are designed for use with eight-ohm speakers and those rated at only four ohms may overtax the ability of the decoder components resulting in failure. Also two eight-ohm speakers wired in parallel result in only four ohms whereas in series they are 16 ohms, which is actually easier on the decoder.
  10. Use a one-watt speaker with a decoder rated at two watts without reducing the volume accordingly.
    Some decoders now provide two watts for speaker power, yet many speakers are rated at one watt or less. To prevent damaging the speaker you should either find a two-watt speaker or reduce the volume setting by half.
  11. Fail to provide protection against voltages spikes and current surges on the track.
    Because of the unique electrical properties of DCC and the relatively large amperages employed, it is possible during on-track short circuits for large voltage and current spikes to occur which can damage decoders. Power management devices such as DCC Specialties’ PSXX and NCE EB-1 and surge suppressors have special circuitry which filters these out preventing damage in most cases.
A locomotive shell with multiple colors of wires coming from a decoder
The decoder is installed and has been tested with patience. Note the Kapton tape being used to hold the wires down instead of electrical or cellophane tape. Larry Puckett photo


3 thoughts on “10 (or 11) ways to blow up a decoder

  1. 12. A small portion of C4 with the appropriate detonator. Care must be taken with this, because too large a portion of C4 will not only take out the decoder, but your railroad and the building in which it is housed.

    13. Driving the DCC controlled loco into a bucket of soapy water. Ouch. However, with the correct amount of soap in the water in said bucket, your loco will come out cleaner than when it went in.

    14. Letting your cat on your layout. Not just cat hair, but a sleeping cat in a tunnel is not a thing to trifle with.

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