FT-A DCC only runs in reverse

[bkarschnik]

I have a Bachmann FT-A with DCC onboard that suddenly will only run in reverse. In forward it does nothing, like it's not getting a signal.  Could the decoder have gone bad? If not the decoder, then what?
Thanks,
Bill

[Jim Banner]

A bad decoder is a distinct possibility.  The motor drive circuit of a decoder is known as an "H-bridge."   It looks like an H with four transistors forming the uprights and the motor across the middle.  Two of the transistors run the motor in the forward direction, the other two run it in reverse.  So failure of one transistor would affect one direction but not the other.  When this happens, the headlight and rear light continue to work normally, assuming they worked normally before.  Before chopping out the old decoder and installing a new one, first try resetting it.  Many decoder reset when you set CV8 to 08, but check your manual.

If it is not the decoder, then it is probably a mechanical problem.  Some possibilities include a wire dragging on a drive shaft/universal joint/gear that binds up the mechanism in one direction and not the other.  Sometimes hair or lint caught around an axle will jam things up in only one direction.  Or maybe there is something in the motor.  This used to be common in the days of open motors, magnetic ballast, and people cleaning rails with steel wool but nowadays it is more likely to be bits of ceramic magnet or plastic jamming a can motor.

Jim   

[the Bach-man]

Dear Bill,
Give the service department a call on Monday.
Thanks!
the Bach-man