Decoder install without a motor

[Mr Z]

I have several models that have a powered car at one end and an unpowered car at the other. Think multiple unit cars or British HST's.

Both the powered and unpowered cars have provision for installing a 6 pin decoder.

I usually have no problem with the motorized car.

The problem is with the unmotorized car. The decoder is there to control the lights. Sometimes the lights will only work in one direction (tail lights work) but not the other (no headlight).

Anyone have any idea how to fix this?

Does the decoder need a load to operate correctly? Can I only use certain decoders for this? I've tried 6 pin decoders from Digitrax, ESU and Zico and I've had similar results with all three.

Martin Z.

[peteski]

The install should be simple as the motorized car.  I prefer using a function-only decoder for that (since, without the motor circuit it is less expensive).  I also like to use the same brand decoder for both ends (but not required).

Programing of function-only decoders might be tricky since there is no motor load to present a load on the programming track. 

Of course it has to have the same address as the motor end decoder.  Also (depending on how the model's internal wiring is done) the "reverse" bit might have to be set in CV29, so the proper set of lights comes on for a given direction.

I wonder if you simply installed the decoder backwards?  Doing that with 6-pin decoders does not harm them, but it does make them behave in a weird way.

[daniel_leavitt2000]

This begs the question... Are there any 6 pin function only decoders out there? Might be something useful to rapido and their Comet project.

[peteski]

This begs the question... Are there any 6 pin function only decoders out there? Might be something useful to rapido and their Comet project.

Yes, ZIMO MX681N, but IIRC the motor pins are wasted/unused, and the blue (common positive) , and the additional functions are only available as solder pads.

[Mr Z]

Decoders are not in backwards. I've installed enough of these to flip it over if it doesn't seem right.

Martin Z

[peteski]

Decoders are not in backwards. I've installed enough of these to flip it over if it doesn't seem right.

Martin Z

Well then, I can't easily explain the odd intermittent behavior. I don't believe that absence of the motor would affect the behavior of the function outputs (but I don't recall if I ever tried that configuration).  Just of of curiosity, how does the decoder behave in the unpowered car when it is installed backwards?

Have you also tried to take the known good decoder from the motor car and tried it in the unpowered car?  Does it behave the same as the other (misbehaving) decoder you had installed in the unpowered car?