If there is a whistle (feedback effect), first reduce the power of the microphones, adjusting the corresponding potentiometers with a screwdriver, until an acceptable level is reached. If the hissing sound persists, adjust the speaker volume to eliminate the problem. If the volume is too low, increase the speaker knob first and then the microphone knob, keeping in mind that clear, noise-free reception is better than reception just before the whistle (feedback). Exclusion of call confirmation on the outside station (B) The confirmation tone can be excluded by turning the switch to OFF.
IMPORTANT NOTE
1) Before replacing the handset, write down the wires from each terminal on the existing unit (an easy way is to cut each core leaving a piece of insulation in place with visible color) twist the unused cores together (so you know they're not in use, don't short them).
2) Some older systems will have a cable with a colored core and a solid white core in this case, mark each core with a marker or tape.
3) Some systems may have loop wiring, you will have 2 cables in your handset (make sure there are joints left, as they can be used by other systems as they can service other apartments in the system).
