Start by removing the 5 small Phillips screws from the back side of the device. There is one in each corner, and one in the middle of the left side, opposite the handle.

Removing the panel reveals what this guide refers to as the front side of the PCB.

Near the bottom right corner where the audio cable comes out of the device, there is an orange plastic strain relief sleeve. It interfaces with two prongs on the back plate. Before putting the plate back on, make sure this is oriented properly to allow the prongs to slide down either side of it, and that the tiny wires going to the press-fit connector are not twisted up.

To flip the PCB and see the back side of it, unscrew 4 additional Phillips head screws that are near the short ends of the battery compartment.

Gently pry up the plastic press-fit connector that connects the 3.5mm cable to the board with a flat head screw driver. The connector and wires are delicate, be careful!

Be mindful of the spring that tensions the handle. Its arm is retained by a small beige tab that sits in the convenient cutout on the PCB. When you lift the PCB, the spring arm will come free from that tab and spring downward. It will catch on the potentiometer knob. Try to hold onto it and release it gently so it doesn't slam at full force into the shaft.

To put the PCB back in, you must tension the spring and get its arm wedged into place against the beige tab. I used a small screwdriver to hold the spring arm while carefully seating the PCB. Following the groove cutout of the PCB with the screw driver holding the arm will slide the spring arm into place against the tab.