There are decoder testers available - I believe NCE offers one, see your dealer or Tony's
Follow the decoder instructions to reset the decoder to factory defaults. If you do not have any instructions. Bachmann decoders are based on Lenz designs, try the Lenz 103 instructions, which you can download.
http://www.lenz.com/products/decoders/olddecoders/le103xf.htm
Generally, but not always:
A "function (only) decoder" has no motor drive, it just controls on-off functions.
A "decoder" controls the motor, and usually has some function controls.
A "sound decoder" usually controls the motor and has sound and some function controls
A "sound only decoder" has sound only, and is usually piggybacked with a decoder for motor control.
Is there anyway to test a decoder? I have an HO Bachmann loco that has a (function) decoder installed by the factory. While trying to set the address and what-not the engine stopped running on any address and I didn't seem to be able to set any variables in program mode. BTW, I have an MRC Prodigy system I tested it replacing the decoder with the jumpers and the engine runs fine on a section of DC track , so now I don't know if I fried the decoder while setting it up or just wiped out all the factory presets(if that's even possible). I know it's not the Prodigy because I have another DCC loco that runs fine on it.
Also, what is the proper name for a decoder that is not a sound decoder? Some times when I post questions about problems with decoders people reply with solutions that they used on their sound decoders and I just want to avoid confusion.
J.P.