ER-301/CPU Board Removal
The Tool (ザ・道具）
You will need something to insert between the CPU board and the main board that will not scratch the PCB surface. My favorite is to wrap 5 wooden or bamboo skewers (the kind used for yakitori) with tape. You can also use a popsicle stick or a plastic tire lever. Do not use a screwdriver!
Remove the rear SD card so that it does not get in the way and insert your lever in the gap between the CPU board and main board about 1-2cm. Slowly and gently pull up on the lever until you see a 1-2mm gap open in the connector.
Now do the same thing from the opposite side, opening the connector on this side just 1-2mm.
Repeat 1 & 2
Go back to the first side, and open the gap a little bit wider. Repeat these steps, switching back and forth, widening the gap a few millimeters at a time. Be patient.
At some point, the connectors will completely and safely disengage. Resist the temptation to pull on the CPU board with your hands!