One of the problems some people run into when wiring a decoder into a loco is not getting the motor isolated from the chassis. If the motor is not isolated, the decoder will smoke the instant you give it throttle.

Some decoders, such as Digitrax's, have a method to check the circuits to be sure that power pickup is not shorted to the motor driver or function wires. This is done when power is first applied to the decoder. If it senses a short circuit it will shut the decoder down except for blinking the lights (if you have the lights hooked up properly). So if the lights start blinking when you put it on the track right after installing the decoder, chances are the motor hasn't been fully isolated. Take it off the track immediately, find the short circuit and fix it.

The short circuit can be almost anywhere - including on a defective decoder. Because of this you can't assume anything. You will have to do a few tests to isolate the offending component. Here are a few tips:

1) If you have a Loy's Toys Decoder Tester, unplug the decoder from the loco or harness (providing the decoder is one that has an NMRA plug or JST wire harness), connect it to the Decoder Tester and test it. If LEDs for the headlight start to blink, the decoder is defective - send it to the manufacturer for repair or replacement. Note that if you unplug the decoder from the harness you'll have to have another harness in order to connect the decoder to the Decoder Tester. Doing this only tests the decoder, not the harness installed in your loco.

2) With the decoder disconnected, or at least the motor wires disconnected from the decoder, you can test the motor for shorts to the chassis. This will require an ohm meter or test light. Test each motor lead to both sides of the loco's power pickup. If you find continuity in any one of these four combinations, find out what's causing it and eliminate it.

3) Just because a loco came pre-wired with an NMRA socket and runs perfectly with the dummy plug, doesn't mean that the loco is OK. The loco can have a short circuit and still run fine with the dummy plug. Remember, the dummy plug is a "shorting" plug. When you remove that dummy plug, you are removing a series of short circuits. BUT if the loco also has a short circuit that parallels one of the dummy plug shorts, removing the dummy plug will NOT remove that other short circuit.

To test a loco that has an NMRA socket: Pins 1 and 5 (opposite corners) are the motor leads. Pins 4 and 8 (the other opposite corners) are the power pickup leads. Check to be sure pins 1 and 5 are not shorted to pins 4 or 8. While you're at it, be sure pins 2 and 6 (the front and rear light functions) are not shorted to pins 1, 4, 5, or 8.

Refer to NMRA plug for information about the pin out of the NMRA socket.

Digitrax's Short-Circuit Protection is not fool-proof. While it can prevent frying of a shorted loco in many cases, there are situations that can get through and fry the decoder. Also, once the test has passed and turned the decoder on, any short circuit that is incurred between the power pickup and motor driving circuits during operation will fry the decoder. This is why it's extremely important to use shrink tube on all wire connections, and to be sure everything is taped down securely so it can't wiggle enough to wear through the insulation to make a short.

Digitrax's decoders have this feature. There's nothing to do to make it work. However, if you want to turn it off, it can be turned off with CV61. To do this requires a system or other method to program CV61 with a value of "04".