I had an interesting fault today where the right joycon wouldn’t connect to the switch when attached to the side but I could attach via bluetooth however every button apart from the thumbstick didn’t work.
Getting it to attach was straight forward enough as all I needed to do was replace the side rail on the joycon as the ribbon cable going into the joycon board had snapped at the connector.
With it now connecting via serial when connected to the switch I decided to do a bit of investigation and a bit of reading (check out dekuNuken on Github for his reverse engineering on the joycons).
First thing I did was back up the SPI files using JCtool on my PC. I then removed the Macronix International MX25U4033E 4 Mb CMOS Flash on the underside of the board near the A,B,X and Y buttons. Remember to remove the white sticky underside of these buttons when using hot air or it will melt. I refitted a new IC from a donor board and it worked!
I then restored the original SPI and all is now good.
Thought I’d share as some might find it useful.