7 tips for installing decoders

7 tips for installing decoders: I don’t know about you, but I have far less hobby time than I would like, so I need to spend what time I do have wisely. Installing Digital Command Control (DCC) decoders isn’t one of those projects I look forward to doing, but it’s a necessary task for operating my HO scale layout realistically.

To help decoder projects go more smoothly, I’ve compiled a list of tips and check points I use when doing most any decoder installation. On the surface, it may seem like I’m pointing out obvious things – steps that you may be tempted to skip. However, if you do them all, chances are good that your decoder installation will work properly on the first try – and that’s a great feeling.

Even though my layout runs exclusively on DCC, I have a DC power pack on my workbench that I connect to my test track as needed. I test all new locomotives before installing decoders. When a locomotive doesn’t run well on DC, you need to determine the cause and fix the problem before converting it to DCC. Though DCC offers some useful features for adjusting motor performance characteristics, it can’t help mechanical problems such as binding gears, out-of-gauge wheelsets, or poor electrical contact.

While you’re testing the locomotive, you should also check the voltage of the bulbs to determine if they need resistors when converting the engine to DCC. If you’re using 1.5V bulbs, you must place a properly rated resistor in series with the bulb, or the lamp will burn out immediately when activated.

If you’re unsure of the bulbs’ voltage, disconnect them from the locomotive and try lighting them with a 1.5V battery (a AA cell will work). The bulbs will light at normal brightness if they’re 1.5V lamps. If they worked when you tested the locomotive but now are dim or don’t light at all, they’re probably 12V lamps.

Another possibility is that your locomotive uses LEDs (light-emitting diodes) instead of lightbulbs. These always require a resistor. If your installation uses LEDs, keep in mind that they are polarity sensitive. They have two leads: an anode and a cathode. The anode must be connected to the positive lighting common wire (blue) and the cathode to the function wire (such as white); otherwise, the LED will not light.

I’ve rarely found a defective decoder straight out of the package, but it can happen, and testing the decoder before you install it saves a lot of guesswork later. Decoders are very easy to test at your work-bench, and DCC suppliers such as Loys Toys and NCE Corp. offer inexpensive testers. You can also make your own. The June 2001 Model Railroader, page 81, featured a homemade tester built by Bill Darnaby.

The cardinal rule in decoder installation is that the motor must be electrically isolated from the rails, and this includes the frame of the locomotive if it’s used to conduct electricity to the motor.

In a DC locomotive, the motor gets its power directly from the rails. On some models, such as the older Athearn engine shown above, the motor receives power directly through the frame. If this connection is not broken, you’ll destroy your decoder when you try to operate the engine on DCC.

Wired installations are the most difficult, but they’re still well within the capabilities of a modeler who has some experience soldering. Wired decoders have no plugs or sockets, just a number of colored wires. The National Model Railroad Association (NMRA) has a Recommended Practice (RP 9.1.1) for the color code.

After the motor wires are isolated, simply connect the power and motor wires following the NMRA color code.

6. Insulate connections

To prevent short circuits caused by exposed wires touching, you need to insulate the connections. I use heat-shrink tubing, shown in the top photo of the page.

Make sure to slip the tubing onto the wire before soldering the connection. Once you’ve made the joint, slip the tubing over the exposed wire and gently heat the tube with your soldering iron or a heat gun. (Hold the heat source close, but don’t touch it to the tube.) The tubing will shrink to fit snugly over the wire and insulate it.

When you’ve finished installing a decoder, test your work before you reassemble the locomotive. Place the engine on the programming track and attempt to read back CV1 (configuration variable 1). It should read 3, which is the default address for all new decoders. If that works, place the locomotive on your main line and run it in both directions (using address 3) and test all the lighting functions. When running an engine that’s disassembled, make sure that the decoder and loose wires don’t touch the rails or the engine’s frame, which could cause a short circuit.

If the engine and decoder function as expected, reassemble the model and program the decoder. With that, you’re ready to move on to another project. As a follow-up, next month I’ll take a look a some things to consider when choosing decoders for your locomotives.