Amp only turns on when cover is grounded

ran into issues with a Kenwood subwoofer amp (kac-8152D). When installing the amp in multiple vehicles and at home with bench test. I run into a problem with the amp powering on with only the standard terminal ground .there is what looks like a second ground witch is simply a screw ,screwed into the chassis ( cover) of the amp. When running a second wire from the gnd terimnal to the screw the amp turns on. Guessing there is a short somewhere or something on the board has came off. Suggestions?

There is an open trace between the ground terminal and the rightmost legs of the power supply transistors. If you remove the circuit board from the heatsink it will be easy to find. To repair it, simply tin some 18 gauge wire and zig zag it across the open part of the trace and solder it onto both sides of the open.