[spinifex]

1. What is the 5 Pin Jumper J3?
2. Anyone know what the 5 Pin jumper J3 does?
3. And why isn't it jumpered?
4. What will happen if I try and use it as a 'line out?'

 

[MindsMirror]

Given its proximity to U2 and U22 (a microcontroller and a CMOS logic chip), I'd say it's probably a serial port for programming, testing, or debugging during design or assembly. Put an oscilloscope on it if you want to see what it does.