B&W ASW850 schematic and repair advice needed

I have three B&W ASW850 subwoofers, one has stopped working and one has developed a short term (2-min) buzzing sound after a couple of minutes of recovering from sleep mode.
The woofer tested good and there is no output from the amplifier.
Who manufactured this amplifier for B&W?
Is there a schematic available as I have a technician willing to repair.
Thank you for any advice
jimbo10494@comcast.net