KB870: Troubleshooting Guide for Digitrax Mobile Decoders

Before sending your Digitrax mobile decoder in for repair try these troubleshooting steps to see if you can “bring it back from the dead” and save a trip to the shop and possible repair charge. As with troubleshooting anything, begin checking what could be wrong methodically. Write down your observations as you work through the list to solve the problem.

The most common "repair" problem we see in our repair department is decoders that are programmed incorrectly.
Many decoders we receive for repair have been programmed with CV values that cause them to seem to have a problem. The good news-bad news is that with DCC you have to be careful what you ask for because the system will give you just that, exactly what you programmed it to do. It's good news if you want to fine-tune your loco's performance. It's bad news when you program a CV by mistake and can't work out what you did! We see a lot of decoders that have this "problem." The moral of the story is that before you send something back for repair, check the programming in your decoder and re-program it if necessary.

Decoder Reset CV08
All current production Digitrax decoders use CV08 as the reset CV. If you set CV 08 to 8 all of the CVs set for the decoder will be re-set to factory default values. If you have spent the time to program a 28 step speed table, you may want to re-set everything EXCEPT the speed table. This can be done by programming CV08 to 9.


Decoder Troubleshooting Steps:

Is the loco on powered track that is connected to your DCC system? Sometimes, the track or the system is the problem. These problems may be present only in some areas of the layout so, moving the loco to another area of the railroad or to your test track may help identify the issue.

If the throttle is indicating that track power is off, turn track power on. Some Digitrax throttles show this indication as a small dot on the throttles. If the dot is not on steady, the track power is off and you'll need to press the power key to turn it on.

Test for adequate track power around the layout with the “Quarter Trick.” If your track does not have adequate power supply to the locomotives, then the DCC signal won't get through either. Take a quarter or screwdriver blade and go around your layout creating electrical short circuits across the rails every 3-6 feet. Your command station will beep and shut down as each short circuit you create is detected (Zephyr & Zephyr Xtra command stations show a blinking display instead of a sound). When the short circuit is removed, the booster will return to normal operation. If this does not happen, then you need to add more track feeders so that the signal/power is adequate all over the layout.

Can you select the loco on your throttle? If not, the loco may be in use by another throttle in this case, your Digitrax throttle will ask you if you want to steal the address. The decoder may be part of a consist (do you see a cn in the display when you try to select it)? See your throttle manual for procedures to release the loco from other throttles or to remove it from the consist so you will be able to run it on your throttle.

Does your throttle display show 'xFF' or ‘FULL’ This means that the system's capacity to handle operating loco addresses is full.

The Zephyr Xtra can run up to 20 addresses at the same time.
The DCS50/Zephyr can run up to 10 addresses at the same time.
The DB150 that comes with Super Empire Builder can run up to 22 addresses at the same time.
When you have selected the command station's limit of addresses in use and try to add another one, the throttle will display ‘FULL’. You will have to release one or more of the addresses currently in use in the command station in order to run another address.

The DCS100 that comes with Super Chief Sets can handle up to 120 addresses at the same time. The DCS100 is set for 22 addresses at the factory. When you have 22 addresses in use and try to add the 23rd, the throttle will display ‘FULL’. With DCS100, you have two options: 1. You will have to release one or more of the 22 addresses currently in use using a throttle in order to run sthe 23rd address. Or 2. You can consult your Super Chief manual for information on changing the number of loco addresses the DCS100 can handle to 120 if you are exceeding the limit often during operations.

During decoder programming, the FF or FULL message may also be displayed if the loco you are trying to program has to many loads attached. If this is the case, you need to remove some of the extra loads to allow the decoder to be programmed. This happens most often with locos that have many lamps installed or where the lamps are wired directly to the track pickups.

Was the loco running and then suddenly stopped? If the decoder is very warm it may be in thermal shutdown. Let it cool off and see if it starts up again. Did the decoder run on to an unpowered section of track? If so, work on the track issue. Is someone running the loco on a different throttle at the same time you are running it? They may have selected the loco by mistake or they may just be messing with you.

Is the loco running more slowly than you think it should? The layout may be underpowered. If you are running more locos than the power you are providing through the boosters, you may need to add more power to the layout. Each booster supplies between 3 and 8 amps of power. Each locomotive and it's functions take from 1/2 amp to 5 amps each to operate. If you are running turnouts and other devices from the same power bus you are using for running the trains, that may be a factor as well.

Are there burn marks on the decoder? If so, you'll need to send it in for repair since the smoke has been let out! If you bought it less than a year ago, make sure to send a copy of your receipt for a no charge repair.

Have you reset any CVs since the last time you ran the loco? If so, you can read back the CVs you recently changed to make sure the setting is correct. If you can't remember what you changed, you can use the reset CV as described above to go back and change them all to their default values and then try to run the loco. It is possible to set acceleration so high that it will take 10 minutes for the loco to start moving and this makes it look like the decoder is not working. If you can't remember the locomotive's address, simply re-program it.

If you are using a non-Digitrax decoder check to be sure the settings in CV29, (the decoder configuration register) match the command station’s output? Digitrax decoders are set up for running on a system that is sending 28/128 speed step commands. If your decoder is a 14-step decoder status editing will be needed to make the commands sent by the system match what the decoder is expecting. See your throttle and decoder manuals for information on status editing.


Strange Behaviors of Locomotive Lights

If your Digitrax decoder blinks the lights when it is put on DCC track for the first time, remove it from the track immediately because this behavior indicates a short circuit in the installation. Check the installation and correct the short circuit to prevent damage to the decoder.

If you have a Digitrax Series 3 decoder and you can control the lights but not the motor, check for a motor short circuit. These decoders are designed to shutdown motor operation when a short is detected to prevent damage to the decoder.

If you can’t control the operation of the lights in your locomotive, be sure that the decoder is programmed to match the speed setting used by your command station. All Digitrax command stations are set for 28/128 speed step mode. All Digitrax decoders are shipped programmed to 28/128 speed step mode. You may have changed your decoder’s programming when performing the decoder test procedure. In any case, if you are not able to turn the locomotives lights on and off, you will need to change CV 29 to a value of “06” to have proper light operation when using a Digitrax command station in its optimum 28/128 speed step mode. Refer to your command station manual for programming instructions. Additional information about programming CV29 is also available in your Digitrax Decoder Manual.

Computer Programs

Another useful tool for analyzing mobile decoder problems are the various computer software products for decoder programming. These programs give you a visual list of the various CV's and the values programmed in a particular decoder, making troubleshooting considerably easier.