HST Sound Decoder Problem: Responds Once Only To Commands In Reverse

[BR(S)]

Before I write my enquiry, I should just emphasise the seller of the sound decoder, Ian Bishop (Legomanbiffo), is helping me with the problem, but I just thought I'd see if anyone else had experienced the problem or can offer things to try.

 

I purchased an HST sound decoder for the power car only and am running it as a single power car.  I have attached it to a large bass reflex speaker and when the power car is running forwards (i.e. headlights on) everything works fine with a nice Paxman sound. 

 

However, when running backwards (i.e. tail lights on), it will respond to commands once (occasionally twice) but then stops responding.  So the motor works fine the first time in both stopping and starting but once it starts running again, the motor continues to move even if the controller has been set to zero, and other functions, such as the horn, won't then operate either.  It will eventually stop moving but can take several minutes.  I have tried setting CV54 to 0 and then pressing F1 but this hasn't done anything. 

 

I've tried the decoder in a Hornby Class 60 and it works fine, so my first thought is a problem with the PCB in the HST.  I've tried it with a non-sound decoder (Hornby R8249) and that works fine.  I've also tried running the decoder in the HST without the sounds on, but the problem remains.  I'm using a Bachmann Dynamis and can't test it on another DCC system.

 

Has anyone ever experienced this kind of problem? 

[pipparooba]

try another non Hornby chip in the 43 lenz or Bachmann and see how it goes if the sound chip works in the 60 ok then it could be a lose wire on the 43 pcb you could try putting the chip in the rear none power unit as it too has a 8 pin slot and see how it works then  

 

hope this helps 

[BR(S)]

Ian suggested removing the capacitor and this seems to have done the trick.

 

I initially tried disconnecting the motor wires (the capacitor is attached to these) from the PCB and the decoder then worked perfectly.  I snipped one side of the capacitor from the wires and reattached the motor wires, but the problem still existed.  Removal of the capacitor from both motor wires seems to have cured the problem.