A Decoder Tester You Can Make

A Simple Decoder Tester


This is a drawing for a very simple decoder tester. All resistors are 1/4 watt unless noted other wise. All parts can be purchased at your local Electronics store or Radio Shack. Yes even the NMRA socket, but you have to do a little work to get it. All you have to do is purchase a Machined Contact 8 pin dip socket, such as the Radio Shack part #RSU 11354180.

A machined contact dip socket has round holes in it instead of the normal flat contacts. Some times referred to as funnel entry contacts. Once you get one all you have to do is cut it in half vertically, this gives you two strips with four contacts each. Just reverse both and epoxy back together. This will make the contacts narrow enough for the plug, and give you a little shelf down both sides to allow you to epoxy it into a hole.

Of course if you have a old PCB you removed from a loco, that has a socket on it, you already have one you can use. Another way to make one is to use the in line dip headers and just cut them to the proper length.


As show this tester will test the motor output via the Bi-Colored LED and also the front and rear headlight functions. If you want to test more functions then all you need to do is add more LEDs and 1k resistors. If you really want to get fancy, you can add a terminal trip with clips so you can just connect the wires from a decoder that does not have a NMRA plug. Or if you want to go deluxe, you can purchase an extra Digitrax harness with Digitrax plug on it and wire it in and connect a LED and resistor to all the extra function wires.

Now you can test just about any decoder you might purchase.


For the power input you can connect this to either the tracks or the booster output to the tracks. You can just solder a couple of gaiter clips on these two leads, and just clip it on the tracks when you want to test a decoder.


The Bi-Colored LED will show direction and speed via color and brightness. The other LEDs will just turn on and off as you turn the functions on and off. Simple to build, simple to use and you will know with out having to install the decoder that it is ok. If something does go wrong with your install, you will not have to wonder is that decoder was bad, or did you do something wrong if you test it first. And with out having installed it, if it is bad you know you can always return it and get another one.