Joy Cons (Nintendo Switch)
The Joy Con main rail between the Joy Con and Switch console is below.
Joy Con Rail
Joy Con PCB
HIGH when connected to console via Bluetooth. Joy-Con will not send serial data post-handshake unless pin is pulled LOW by console.
Joy-Con power and charging
Joycon Inverted level (idle at GND)
Joy-Con reset signal , high level is reset. Ground when console is awake
Standard level (idle at 1.8V)
Joy can output power to Ring Fit Adventure or starlink toy
Joy-Con will only send data to console when this line is HIGH
More details on the protocol and interface can be found here.
The Joy Con battery charges through a BQ24073/4 charger IC.
The battery comes in to the BAT pin of the BQ charger.
The output from the battery to the Joy Con comes out of the OUT pins.
The 5V to charge the battery comes in through the rail FPC connectors pin 2 (5V), via a fuse.
To check the charger is working, first check the fuse is good, and when you apply 5V to the test pad, the bench should show current being pulled that is charging the battery.
Make sure the fuse is good, and the 5V goes into the IN pin of the BQ chip.
Confirm the battery voltage is good (positive is top pin), and that the battery voltage (3.3 to 4.2V) makes it into the BAT pins of the BQ charger.
To understand more about how the charger should operate read each expected pin description below.
I will do a deeper dive and guide on testing the charge circuit when I get time.