DCC troubles

[Gene P.]

Hello!
I have an Athearn F59PHI to which I have added a Digitrax decoder. Nothing fancy, no sound. The lights work, and switch properly from forward to backward as the Locos direction changes. However, it only moves in the reverse direction. It will not go forward. Any advice?
Thanks in advance!

[TomKat]

Gene, I am first getting into DCC myself, but the man you need to talk to is Jim Banner. Send him a personal message here in the forum email and he'll get back to you. The man is very knowledgeable when it comes to any train locomotive.~TomKat

[Jim Banner]

Thank you for the kind words TomKat - enough to make me blush!

A defective decoder is always a possibility but first check for errant wires.  Sometimes a wire ends up next to a rotating part of the mechanism and jams it up when it tries to run in one direction but not in the other.  This shows up pretty quickly when you run the locomotive with the shell removed.

Before talking about other possibilities, what decoder did you install in your Athearn 59PH?

[Gene P.]

Thanks for the responses!
The decoder is a short wire Digitrax 123. It worked fine in another loco I had installed it in originally. I was hoping it would be a CV setting. I'll pull the shell and look for stray wires over the weekend.
Thanks again!

[Jim Banner]

The Digitrax DH123 decoders have scalable speed tables.  Speed tables, if turned on, set the relationship between throttle position and speed.  Scalable means you can easily shift the table for a great or smaller speed range by using two trim CVs, one for forward speed and one for reverse speed.  If you are using the speed table, make sure CV66 which controls the forward trim is set correctly.  If in doubt, set it to 00  (off).  While you are at it, do the same to the reverse trim control, CV95.  An alternative would be to set CV29 to its default value of 06 which turns off the speed table.  A more drastic alternative would be to set CV08 to 08 which should resort all the default settings of the decoder, including the speed table and the trim controls.

Depending on the DCC command station you are using, it may or may not be possible to read back or even program these CVs.  In that case, you may have to enlist the help of a friend, a club or a hobby shop.

There are other possible causes for your problem.  I once found a plastic arm from an engineer inside a can motor.  No idea how it got there (the engine crew had all their arms intact) but it caused some strange problems, including sometimes operating in one direction but not the other, before destroying the motor.  Solder or copper traces on the adapter board in the locomotive can also cause weird electrical problems, although I am not sure it could cause this one.  And some boards require that you cut a trace or two when installing DCC.  Usually such traces are indicated by an X across them and if you do not cut them, strange electrical problems occur.  Hopefully, your problem will be easier to solve.