Loco only runs in one direction, and at full speed.

[darkscot]

I have a Bachmann Webb coal tank loco that has been running fine on DC. I have run it on DCC, but switched back to DC while I sorted my track out.

Today I refitted the decoder (Zimo Next18) and tried to run it. However, no matter what setting the controller is it will only run in one direct, and at full speed. Adjusting the control knob has no effect on speed or direction. I have tried two different DCC controllers and it is the same with both.

Is there possibly some CV setting that has got corrupted?

[brian1951]

have you got the decoder fitted the correct way.

[darkscot]

I didn't think you can fit Next18 decoders the wrong way? Anyway, if you fit it the other way round the decoder would stick out the front of the loco.

[brian1951]

People have fitted decoders one pin out, i have seen all sorts. It sounds like you have a corrupted signal and its picking a DC current, so firstly disable DC running with CV 29. Do not alter any other CVs. And as always make sure track, wheels and pick ups are spotless.

[RFS]

Sounds to me there's a problem either with the decoder or the socket, and track power is being fed directly to one of the motor terminals. Do you have another decoder you can try?

[cadman]

You will probably need to reset the decoder to it's default values such as address 03. This should clear any corruption......HB

[Goingdownslow]

On my Coal Tank I had to remove a fixing screw from the pcb that was contacting the bottom of the decoder.
I did this before running it so I don't know it's effect.

[darkscot]

On my Coal Tank I had to remove a fixing screw from the pcb that was contacting the bottom of the decoder.
I did this before running it so I don't know it's effect.

Well that is interesting?

[darkscot]

Well got my SPROG II out of storage with the intention of doing a reset on the decoder. However, prior to doing that I gave the decoder plug a gentle clean and low and behold it now works!
I also took a look at the fixing screw previously mentioned and it does get perilously close to the circuit board. However, with the Zimo decoder it is not too close to metal parts.

[RAF96]

Next 18 is almost foolproof by being reversible. The pins are mirrored in duplicate to handle the electrical loads.
Most runaway problems are due to DC running being enabled in CV29.
In this case a dirty or intermittent contact could disrupt the DCC signal resulting in the decoder going into DC mode and realising full track potential.