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The FRITZ!Box's Power LED flashes

As soon as you connect your FRITZ!Box to your DSL line, the FRITZ!Box establishes a connection to the DSL provider's exchange. This can take up to 10 minutes. During this time, the Power LED on the FRITZ!Box flashes and then stays lit as soon as the DSL connection has been established.

This guide shows you how to resolve the following errors:

  • The FRITZ!Box's Power LED flashes continuously.
  • The FRITZ!Box does not establish a DSL connection.

The following error message is displayed in the event log of the FRITZ!Box:

  • "DSL not responding (no DSL synchronization)"

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

Note:All instructions on configuration and settings given in this guide refer to the latest FRITZ!OS for the FRITZ!Box.

1 Checking the event log of the FRITZ!Box

  1. Click "System" in the FRITZ!Box user interface.
  2. Click "Event Log" in the "System" menu.
  3. If the message "DSL is available (DSL synchronization exists with [...] kbit/s)" is displayed in addition to the message "DSL not responding", follow the steps in our guide FRITZ!Box reports that the DSL connection drops frequently.

2 Making sure that the DSL line is supported

The FRITZ!Box supports all DSL lines that are common in Germany, Austria, and Switzerland. The following step is only necessary if you are using the FRITZ!Box in a different country:

3 Selecting the DSL standard

  1. Click "Internet" in the FRITZ!Box user interface.
  2. Click "DSL Information" in the "Internet" menu.
  3. Click on the "Interference Resistance" ("Line Settings") tab. If the tab is not displayed, enable the Advanced View first.
  4. In the section "Annex Settings", select whether your FRITZ!Box is connected to a DSL line that uses Annex A or Annex B.

    Note:In Germany, Annex B is always used, other countries almost always use Annex A. Contact your DSL provider to find out which standard is used on your DSL line.

  5. Click "Apply" to save the settings.

4 Checking the DSL line and cabling with the DSL line test

Performing the DSL line test

Links to "Contents" and then "FRITZ!Box Support"
  1. In the FRITZ!Box user interface, click "Contents" on the bottom left of the page and then "FRITZ!Box Support".
  2. Click the link "DSL line test".
  3. Remove the DSL cable from the FRITZ!Box.
  4. Click the "Calibrate" button and click "OK" to start the calibration.
  5. Reconnect the DSL cable to the FRITZ!Box once calibration is completed.
  6. Click the "Measure" button and click "OK" to start the DSL line test.
  7. Work through the instructions in the section matching your result.

Line test reports: DSL cable defective or not inserted

  1. Use a different DSL cable (for example from a different DSL modem) to connect the FRITZ!Box to the socket labeled "F" on the telephone jack.
  2. If the Power LED lights up constantly after 10 minutes, the DSL cable used before is defective and must be replaced.

    Note:You can either purchase a new DSL cable from an electronics retailer, or order one from us by sending an email to You can also make your own DSL cable using the guide Assignment of cables, adapters, and sockets.

Line test reports: Error in on-site wiring

  1. Remove the DSL splitter if you are using the FRITZ!Box on an IP-based connection.
  2. Remove all cable extensions, unused cables, telephone jacks, and additional electrical components (for example surge protection, automatic extension outlets).
  3. Insert the DSL cable (Y cable) into the "VDSL" socket on the FRITZ!Box.
  4. Insert one of the two shorter ends of the cable into the DSL socket and leave the other end of the cable hanging. If you are using the FRITZ!Box on a VDSL bonding line, also insert the second end of the cable into the VDSL bonding socket.
    Connecting the FRITZ!Box to an IP-based DSL line (left) or a VDSL bonding line (right)

Line test reports: Error with provider

  1. Either: Test whether a different DSL modem works on your DSL line.
    • Or: Test whether the FRITZ!Box can establish a DSL connection on a different DSL line, for example at your neighbor's.

      Note:Only connect the FRITZ!Box to the DSL line and the power mains. A DSL connection was established if the Power LED remains lit after no more than 10 minutes.

  2. If another modem also does not work on your line, or if your FRITZ!Box can establish a DSL connection on a different line, then there is a problem with your DSL line. Contact your DSL provider and have them check your DSL line.

    ATTENTION!You may be charged for checking. Ask your provider about charges in advance!

5 Installing the latest FRITZ!OS for the FRITZ!Box

Installing the latest FRITZ!OS makes your FRITZ!Box compatible with the latest DSL technology used by DSL providers in their DSL exchanges: