Evan, since I have two RPi4s with damaged SDA and SCL GPIO pins and another with a damaged GPIO4 (TX) pin I think I should put 3.3 volt Zeners on those lines, with series 330 ohm resistors. I assume the LC changes won¡¯t be significant enough to interfere with the edge detection for the I2C bus. The best place would be at the exposed right angle bend in the 40-pin brass connector J2 mounted on the digital board. A cut there would allow for a series resistor insertion, and there is an adjacent ground plane on the digital board for the Zener diodes. Incidentally the WM8731 codec pins, 19 RLINEIN and 20 LLINEIN already have 3.9V Zeners! I wonder how delicate those inputs are.
Jack
N6LN
John Terrell, N6LN