You do not need to replace the whole back plate. First verify that the bias power supply is in fact the problem by swapping the left channel backplate with the right channel. Then take pictures of the back backplate and email them to Dr West. He will guide you in the diagnostic process. He will look for the spare components that you need to replace and ship them to you if you choose not to send the whole backplate in for repair at the factory.
Most likely the bias supply is defective, I would contact the factory for further advice and obtaining a replacement supply.
You might want to replace the bias supply in both backplates with the latest version as the supplies are now regulated and will maintain proper bias regardless of line voltage variations.
I hope everyone is doing well. I haven’t been listening to my system for about a month and when I turned it on today, one side was not making any sound. I switched the backplates and now it is the other side that is not making any sound. The backplate that is not making any sound doesn’t crackle when I turn up the bias. I just hear a hum. Does anyone know what could be wrong.