These decoders are made to fit specific locomtoive chassis.  Locomotives that have circuit boards that can have decoders installed in place of the original circuit board are made by many manufacturers.

In some cases, locomotive modifications, motor isolation and additional soldering may be required during installation of this type of decoder.  Function leads can be added to these decoders using solder pads available on the decoder.

See the instruction sheet for the particular decoder you are using for specific instructions.

Sometimes these are called plug n' play or drop in decoders.

Digitrax Real FX³

• Turn functions on and off. 
• Head lights and tail lights are automatically reversing unless you make them independent. 
• All function outputs have FX generators for prototypical lighting effects and have qualifiers for FX effects and qualifiers for standard on/off functions.
• All Digitrax Series 3 decoders have FX³ type functions.
• FX³ decoders offer full function mapping so you can choose which function (F0-F12) controls each function lead.
• FX³ decoders offer master light switch capability.
• FX³ decoders offer qualifiers for FX function operation qualified by one of the following:  the loco's direction of travel, whether F0 is on or off, loco direction and F0, or whether the loco is moving or not. These qualifiers are also available on function outputs that are used as standard on/off functions.

Series 3 decoders with 6 functions have FX³ function outputs

Torque compensation

SuperSonic motor drive for quiet operation (silent operation)

Support for all DCC programming methods as of the time of release

Operations mode read back capability for CV read back on the main line

Scaleable Speed Stabilization (Adjustable Back EMF)

One Step decoder Factory CV reset (CV08=8 or CV8=9 to preserve loadable speed tables)

Motor Isolation Protection

Transponding

White or Golden Yellow LEDs on decoders that come equipped with LEDs

Series 3 decoders with less than 6 functions have a modified set of features

Digitrax gives a one year "No Worries"Warranty against manufacturing defects and accidental customer damage

on all Digitrax command stations, boosters, throttles, decoders, power supplies and layout control devices.