No PWM Output from PX4

Hello, I am trying to set up a new PX4 for use with a quadcopter, but it does not seem to output any pwm signals even when armed (and QGroundControl says “takeoff detected”). I can detect PWM output raw from the receiver PWM outs using a multimeter, but neither I/O or FMU PWM outs seem to send any signals. Any idea why this might be happening?