Sony TC-K390 - autostop triggered randomly while playing any tape

Got a Sony TC-K390 that randomly triggers the autostop mechanism, I checked a little bit but I can't figure out what and where is the fault. All belts and pinch roller replaced. Can't see if there is a idler tyre there, most probably not. It gets triggered sometimes after 10-20 seconds of play, other times after 1-2 minutes. Any advice please?