Piezo not working on SS Hollow Body?

I haven’t used this function in years and took out the battery a while ago to use it in a stomp pedal at a gig. Anyway, the normal input jack was getting loose recently so I removed the cover on the back so I could properly hold it from the back while I tightened it. Lo and behold I saw that there is an adjustable preamp unit inside (I discover this after years of having the guitar!). So I want to try it out. Put in fresh battery but – nothing. No sound from the guitars piezo when plugged into either jack, the blended or the direct. Any ideas?

Heres a pic. Shes the only guitar I put back in the case every single time I play her. Last thing I set up at gigs and first thing packed. She looks the same as the first day I got her aside from the neck darkening from hands and lemon oil.

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