Performing an ADSL Isolation Test

What is an Isolation test?
An isolation test is one of the fastest ways to determine whether a fault lies with your equipment (eg: telephone handset, ADSL modem, incorrect filtering etc.) or with the phone line. It is a crucial test before lodging a fault with us and in general, if you contact us regarding a problem with either your ADSL or phone connection, our staff will ask you to perform it.

Isolation tests are commonly performed when your ADSL connection seems to lose synchronisation intermittently, drops out completely or when you are experiencing slow speed.
Isolation test for ADSL in 3 simple steps
  • Start by removing all equipment connected from your phone line that the broadband modem is connected to. This includes telephones, fax machines, line splitters and anything else that uses the same telephone line in your premises (multiple wall phone sockets).
  • Once you have disconnected everything, connect your ADSL modem directly into the telephone wall socket using a telephone cable that is no more than a metre in length. There is no need to filter this cable. Turn on the modem and observe the DSL sync light.
  • If the modem failed to attain synchronisation (most modems display this with flashing DSL light) after a few minutes, turn the modem off for 30 seconds and turn it back on again.

  • Note: You may check the wall socket you are using for dial tone by connecting a telephone using the same cable to ensure the telephone line is working. Alternatively, check other wall sockets in your premises.

    If synchronisation is successful

  • If the modem does achieve synchronisation, it would appear that the fault would be a CPE (Customer Premises Equipment) issue and you will need to perform One-at-a-Time test to narrow down the possible cause of the fault.
  • Start plugging back in each piece of equipment with a filter one at a time. Wait for a few minutes and observe the DSL sync light before proceeding to the next piece of equipment. If synchronisation goes off, it is possible you may have found the equipment that is causing the problem.

  • If synchronisation is unsuccessful

    If the modem fails to achieve synchronisation, if possible, try:

  • Connecting with another modem to determine whether it is a modem fault.
  • Connecting modem to another wall socket in your premises on the same telephone line.
  • Check for dial tone on the line the ADSL service is installed on.

  • If still unsuccessful and your modem is definitely in good working order, it would be a good time to call our support team to check if there is any outage in your area or to lodge a possible fault. Please remember to let them know you have performed an isolation test.