Hornby sound decoders

You might try resetting the decoder. Answers elsewhere say that resetting CV8 to value 8 will reset the whole decoder but will not cause any damage. To reset just the sound it is value 5 to CV8.
It confirms that in the instructions which come with the models. Page 2 - top right.
If you have mislaid the Manual, it can be downloaded here
https://support.hornby.com/hc/en-gb/articles/360016158839-A1-A3-Sound-Decoder-Manual

Julian

I just re-read your question again and I'm not sure that CV8, decoder resetting is the solution. A few questions might bring a different answer.
1. I note that you said that the sound was lost on all the decoders. Did that happen all at the same time, ie. so they all worked fine and then none would work?
2. Do the motor commands still work ok?
3. Do any of the other function sounds work at all?
4. Was there some event that occurred just before they all stopped working?
If the answer to Q1 is yes, it may be the PowerCab which could need a reset. Their instructions for resetting the PowerCab are at https://ncedcc.zendesk.com/hc/en-us/articles/201251979-Reset-Powercab-to-factory-defaults

Hope this helps.
Julian