What to check

In the telephone check that the wire going to the "F" terminal is making a good connection and that this is also linked to terminals "B" and "G".

Corrective Action

Ensure good connection at "F" "B" and "G"

Additional notes

The "F" wire is the common for speech both ways and, when linked with "B" and "G", which it is on most systems, it is the common for all phone functions.

In a properly functioning system, there will be DC voltage between "F" and "L","F" and "P" and an AC voltage between "F" and "1"