As far as electrical shock hazard its no different than any other electronic device...make sure it is unplugged from mains power. There is typically some charge that remains in the power supply filter caps, but that should drain pretty quickly.
The monitor amplifier PCB isn't a plug-in PCB, so you can't re-seat it like the PCBs in the upper cardbay. You *can*, however, re-seat the *connections* to the PCB. Tip the machine on its side and remove the bottom cover to access most of the connections, including the buss PCB that spans across the bottom of all the mixing section PCBs. Any connections you can't readily get to (if any...can't recall off the top of my head) may require removing adjacent PCBs, or partial removal of the monitor PCB itself (remove the buss PCB, all connections you can access, remove the pot nuts and any screws fastening the PCB to the dress panel, and slip it down as far as it can go to hopefully access any remaining connections).