Aria swb 4 no sound

Hi Folks, I have a used Aria swb 4. It has been working great for the last year and a half. Suddenly, there is no sound. I have replaced the battery. Nothing. I have tried different cables, nothing. When plugged into a pa with the master volume cranked, there is a hum, but no string noise. I have dismantled the controls and the jack and everything is connected. Anyone have one of th we or know what I should be doing to troubleshoot? I have emailed Aria in the U.K. Twice, but no responses.