Panasonic KX-TCD420GS Service Manual page 25

If the known working telephone still has problems, then please contact the customer service
department of your Network provider.
If it operates correctly, then the problem is likely to be a fault in your apparatus.
In this case, contact your supplier for advice. Your Network provider may charge you if they attend a
service call that is not due to apparatus supplied by them.
Turn the power OFF then ON (Handset) / Disconnect then connect the AC adaptor (Base Unit).
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