Reversing section diagnosis with a test light

Previously, the basic operation of a test light was discussed. In this post, the use of a test light will be employed to diagnose issues with a reversing section.

DCC reversing sections are placed between two sections of fixed-phase track. The phases are opposed, so a short would occur without the autoreverser. The autoreverser works by sensing a short and flipping phases to correct the problem. As long as this works, operators don't notice a thing. When this fails, trains will often work correctly until the crossing between the opposed fixed-phase track and the reversing section.

The test light can be used to indicate which phase the rails are connected to at the moment. Connect the test light to one rail in the fixed section and one rail in the reversing section. If the light lights, you know the rail is the opposite phase of the one connected to the test light. If the light doesn't light, it's probably a good idea to check the other rail just to make sure the connection is good.

To test the reverser, a momentary short must be created. If the test light you're using has a long probe, it can be used to bridge the rails to create a short. At this point, the reverser should flip polarity (check by repeating the test above.) Sometimes the reverser flips multiple times, or faster reversers (such as the PSX-AR) may see the short for too long and not change polarity. If this happens, another way to trip the reverser is to use the test light to bridge an insulating gap. A test light with a long probe can be used to bridge the gap.

If the reverser does not trip, start looking for the trouble in the end that's working fine. Most likely, something is closing or bridging the gap.

If needed, power can be strategically removed to help isolate the trouble area. By disconnecting power to the fixed section, then looking for current to flow from the reversing section to the fixed section, the rail that contains the short can be located. For example, if the test light is connected to Rail A and Rail B in the reversing section it should light. Keeping one end of the test light in the reversing section, move the other out into the fixed section. If the light lights, that rail is receiving power from somewhere.

Once the operation of a test light is understood, it can be a very useful tool in troubleshooting. Troubleshooting can be described as the process of eliminating what works properly in order to reveal what does not. The test light is an excellent tool for doing just that.