Lock/sleep button not working

Hi everyone,

I have just replaced the lcd and digitizer on a ipad mini 2. The lock button has now stopped working. It will turn the device on and wake it up but i cannot lock the device or turn it off. I can hild the home and lock button down together to do a soft reset which hasnt worked. I disconnected the battery first so dont think i have shorted anything. The digitizer came with everything on it so no soldering. I have tried 3 different digitizers. I have taped up the terminals on the back of the digitizer to prevent ghosting and have tried lifting the digitizer slightly but it still wont lock. I have tried assistive touch and that wont lock it. I have tried turning off the ipade case lock and removing the passcode.

I repair these devices daily and am at a loss as to wht i should try next.