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Knowledge Base document #73

Phone connected to FRITZ!Box is dead and/or phone system indicates a malfunction

A phone connected to the FRITZ!Box is dead and/or a phone system (PBX) indicates a malfunction:

  • When you pick up the handset of a phone connected to an analogue extension or the 'FON S0' socket on the FRITZ!Box, you do not hear anything (for example a dial tone or busy signal). The phone is 'dead'.
  • The display of an ISDN phone system connected to the 'FON S0' socket indicates that there is a malfunction.

Simply proceed as described below. After each measure, check whether the problem is solved.

1 Plugging the FRITZ!Box in

  1. Plug the FRITZ!Box into a socket where other devices work.

2 Setting up an analogue phone

Only one FON socket can be used

'FON 1' has two options for connecting devices: An RJ11 socket and a TAE socket. You can only use one connection option at a time:

Example:
If you connected a phone to the RJ11 socket for 'FON 1', you cannot connect a device (for example a fax machine, answering machine) to the TAE socket.

  1. If you connected devices to both of the sockets for the same extension, disconnect one of the devices from the FRITZ!Box.

Testing a different analogue phone

  1. Disconnect the phone from the FRITZ!Box.
  2. Connect a different phone to the same socket on the FRITZ!Box.
  3. If you hear a sound, then the first phone is defective or the phone cable is damaged or incorrectly wired. Test a different cable or contact the manufacturer of the phone.
    • If you do not hear a sound, check whether the plug of the phone is correctly wired. The two inner pins carry the analogue signal of the RJ11 sockets of 'FON 1' and 'FON 2'.

3 Setting up ISDN devices

Properly connecting ISDN phones and other ISDN devices

  1. Always connect ISDN devices to the 'FON S0' socket of the FRITZ!Box.
  2. Do not use ISDN cables that are longer than 10 m.
  3. Do not connect more than one ISDN device that must be supplied with power from the FRITZ!Box. You can connect a total of eight ISDN devices to the FRITZ!Box.
  4. Only use ISDN devices that are suitable for use on a point-to-multipoint line.

    Note:Point-to-multipoint ISDN lines are common in the private sector and in small businesses, while ISDN BRIs are used in professional environments.

Connecting ISDN phones and other ISDN devices individually

The following steps are only necessary if two or more devices are connected to the 'FON S0' socket:

  1. Remove the ISDN distributor and all ISDN devices including their cables from the FRITZ!Box.
  2. Test each ISDN device individually and attach it directly to the 'FON S0' socket (without an ISDN distributor).
  3. If all ISDN devices function properly when no other ISDN devices are attached, test a different ISDN distributor.

Testing a different ISDN phone

The following steps are necessary if only one device is connected to the 'FON S0' socket:

  1. Connect a different ISDN phone (for example from neighbours, friends) to the 'FON S0' socket on the FRITZ!Box.
  2. Check whether the phone makes a sound (for example a dial tone, busy signal) when you pick up the handset.
  3. If you hear a sound, then the first phone is defective or the phone cable is damaged. Test a different cable or contact the manufacturer of the phone.

4 Restarting the FRITZ!Box

  1. Click on 'System' in the FRITZ!Box user interface.
  2. Click on 'Backup' in the 'System' menu.
  3. Click on 'Restart FRITZ!Box' and then on 'Restart'.
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