To put your Frigidaire Gallery refrigerator in diagnostic mode, follow these steps:
1. Remove the control panel.
2. Take out the main board.
3. Replace the main board.
4. Connect all wires.
5. Install the new interface.
6. Secure the lower trim.
7. Plug in the power cord.
For detailed instructions, you can refer to instructional videos on YouTube or consult the Frigidaire website.