DCC Decoders with Class 43

[Stainmore Summit]

I hope someone can help me with what I assume is a very basic question. Having only recently purchased a DCC controller after many years running DC ever since Hornby abandoned Zero-One in the 1980s, I am still trying to figure out basic programming of the decoders. I purchased a Digitrax Zephyr Express as I seemed to one of a few that actually had a descent information display. I recently purchased a slightly secondhand Hornby Class 43 fitted with DCC decoders in both the power car and dummy car. Not knowing what number the decoder as set to I put the power car on the programming track and got the controller to interrogate it, that was fine. When I tried doing the same with the dummy car on the programming track the Digitrax could not see a DCC chip. Tried a different chip, same problem, tried that chip in another loco it worked fine. I thought it might be a fault with the board so I obtained a new one and still the problem persisted. Can someone explain to me why it can’t see the chip in the dummy car to program it? When I put the dummy car back on the running track, the lights work as they should under DCC control.  I do not know what decoders there are, there is no name on them, but the two decoders where the same make. Any information would be of great help as I still clearly have a lot to learn

[Chrissaf]

Many decoders require a motor load to be present across the motor output of the decoder before it will accept being programmed. This is because the programing software code sends a pulse to the motor to complete the software process task. If the motor is not physically present, this final programing check fails and thus the requested software task is not accepted.

This is why the decoder worked when fitted to a different loco (presumably one with a motor) and why a replacement decoder and replacement PCB made no difference to the dummy car programming attempt. When dealing with dummy motor car decoders, the normal methodology is to program the decoder in the motored car first, then physically transfer the decoder to the dummy car afterwards.

Some decoders when used with some controllers allow dummy car programing when placed on the programming track concurrently with the main motor car at the same time (this of course assumes that the same decoder programing is required in both decoders). But as this is decoder and controller dependant, the methodology first described above using the main motor car to program both decoders is more likely to work with greater reliability.

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[ColinB]

I think I did read from someone that putting a resistor across the terminals that feed the motor works. I have no idea of the value but something under 100 ohms I suspect might work.

[Stainmore Summit]

Ah thank you that explains a lot. I am only new to this so have not got as far as understanding consisting yet as I assume that is what I should be using for a loco and dummy car working together.

[Chrissaf]

Not necessarily, consisting is where two motorised cars / locos with different DCC Addresses are configured to operate as one. In a situation where you have a motor car and a dummy motor car both fitted with a decoder, then it is more normal to give both decoders the same DCC Address, this is not technically the same as 'consisting'.

There can be odd occasions when it is desirable to give both decoders different DCC Addresses and operate as a 'consist', but this is usually only used as a 'last resort' to achieve a specified operational requirement that can't be easily achieved through any other method.

In your motor car / dummy motor car situation. You would normally give BOTH decoders the SAME DCC Address (as stated before, this is not a consist). Let's say you want to turn on directional lighting (typically sending a F0 command). You would call up the DCC Address you have configured both decoders with. Then with that DCC Address selected, you send the F0 command. BOTH decoders would be listening for commands for their DCC Address, BOTH decoders will therefore respond to the F0 command because they have the same DCC Address and turn on their directional lights. The wiring (decoder white and yellow wires) in the dummy motor car is usually wired in reverse to the front motor car, so that the displayed directional lights colours are reversed. For example when front lights are white, the rear ones are red and vice versa.