Bachmann 9f DCC problem

[5xp45593]

Hi,

I’m having an issue with my 9f where it will run perfectly fine on analogue however when I fit a decoder to it in order to make it DCC the loco begins running when on the track even though the dial hasn’t been turned up to do so. I use the Hornby DCC elite and do not think it’s any fault with the controller as I run all my other DCC models with it however this one is being stubborn and I’m out of ideas as to why it’s playing up like this as I’ve never experience this sort of behaviour from a loco before. I’ve tried 3 different decoders in which are all giving the same result and I was wondering if anyone can help me with this issue?

[Chrissaf]

Being a Bachmann can we assume that it has a 21 pin decoder socket?

Please be specific with regard the three decoders you have tried - brand and model number - if not known can you post a close up photograph of the decoders.

Not wanting to disrespect your posted comments, but your documented observations would be compliant with a 21 pin blanking plate being fitted and not a decoder and as you have very little posting history it is not easy for us to assess your skill level. Either that or there could possibly be a serious wiring fault with your loco.

One other cause of your observations is that the decoders you are using are not seeing a clean DCC signal and switching into 'DC Operation' mode, thus what you are observing is 'DC Runaway'. To discount or prove 'DC Runaway' use your Elite to modify the value of CV29 to disable 'DC Operation'. This online calculator will assist in defining the new value to write. If with 'DC Operation' disabled you still observe your issue then that would point more to a loco wiring fault, but the track suggestion below should not be ignored.

DCC CV29 Calculator

Are you using Hornby track, if so are you using Hornby track power connectors. If you are, open them up and check to ensure that there are no analogue suppression capacitors inside them. Also if using any R8201 link wires, check inside their connectors too. Remove any and all capacitors you find and test your loco again. The capacitors distort DCC signals and can cause all sorts of 'odd' operational effects to be observed.

This is a long reply with an image. Therefore it is better to reply using the 'Reply' text box at the bottom of the page. The blue button with the white arrow should be avoided as this is not a 'Reply to this post' button.

[5xp45593]

The loco has an 8 pin decoder socket and the decoders I have used is a lais DCC one, a Bachmann 36-556 and a different one in which I believe is Hornby but I couldn’t be too sure. I’m not excellent at repairs or fault finding as I’ve never really came across any but I’ll have to check CV29 and the capacitors in the power connector once I am home.

[96RAF]

I will have to check my notes to see if there was a fix, but I seem to remember that model of B’mann decoder has a history of problems with Hornby and some other make controllers.

I have a poor opinion of Liaisdcc decoders but that is a personal view, not shared by everyone.