Buzz on audio

Audio noise is typically caused by ground loops or poor grounds. To start trouble-shooting remove the PVBX from the equation. Take the audio video coming from a camera where it plugs into the PVBX and instead plug it into a TV. Do you have noise now? If not go to the next cable from another room and repeat to make sure all runs from classrooms are clean. When you find a noisy run, try these steps to isolate the problem:

1. Try different A/V cables, a bad cable at either end can cause problems, and I have seen this with PIs cheap cables

2. Connect a TV directly to the camera in the room, you will get feed-back squeal if you turn the volume up too high, but at low volume there should be no hum. If there is hum, swap out the camera; try powering the camera from a separate AC adapter. Make sure the A/B box is set internally to 12Volts (jumper completely to the end, when you open the case up)

3. Look at the video modulators, (swap out each A/B box, one at a time). Each modulator was tested before shipping, but stranger things have happened.

4. Is the run punched down correctly? Crossed wires will put DC on the audio or video.