What to check
Check the volume setting of door panel amplifier.
Please note - there are two types of amplifier;
3 terminal - marked E, D and C
4 terminal - marked +, -, E &D
NOTE: 'C' and '-' are the same and the terminal marking may be either or both.
For 3 terminal units, the volume is set by the DC voltage output of the power supply. The normal voltage setting is 9V; the higher the voltage the higher the speech volume.
4 terminal units have separate speaker and microphone volume adjustments on the amplifier board itself. Factory setting speaker volume is set at about 1/3 (turn clockwise to increase the gain).
Corrective Action
Adjust volume as required. Either with pots on 4 terminal amplifier or for the 3 terminal amplifier by setting the DC output in the power supplying accordance with the table printed on the label on top of the transformer.
Additional notes
3 terminal part ref: 92ETXAMP (pre 2015)
4 terminal part ref: 10ETXAMP (2015 on)
Links
https://www.entryphone.co.uk/shop/productdetail/PCB-10-ETXAMP
https://www.entryphone.co.uk/shop/productdetail/ETXAMP-3