Graz

I have BT Infinity at home albeit sold to me by PlusNet, got a strange problem.

When I first got the service a year or so back the BT bod came along, plugged his tester in to check the line, fitted the new faceplate adapter to my master socket, plugged in the Openreach modem and away it went.

At the time I asked about connecting an extension I already had run in CAT5 cable so that I could relocate the modem to a bedroom I used as a study / office (i.e. where all the computers were), whilst he muttered something about only be able to use the proper BT extension kit he also showed me where to connect my extension on the master socket adapter so no problem I'd sort it. After he was gone I connected up the extension, moved the modem into the bedroom and it all worked.....

So now with two kids I've had to give up the study so my lad can have it as a bedroom. I don't want the modem / router / etc. in that room anymore so decided to move it all back down and hook it back up to the master socket. Easy enough or so I thought.

Plugged in the Openreach modem into the dedicated socket on the faceplate and it won't connect, the DSL light just keeps flashing on the modem, should go solid when its connected. Plugged a phone into the DSL socket and I get dial tone so there is a circuit there. Took the socket apart and checked the polarity, weirdly the polarity on the extension seems to be reversed, i.e. the A terminal reads -50V. Wonder if the master socket polarity is wrong but probing on the back of there it seems correct, i.e. the B terminal has -50V on it.

Now I've had to remove and reconnect the master socket while we were having some plastering done. I know you're not supposed to touch it as it belongs to BT but personally as I work with telecoms and have a degree in electronics I think I'm probably over qualified to disconnect two wires, be careful not to short them, and later reconnect them. Anyway I start to wonder if the polarity was reversed when the BT chap installed the modem, the faceplate swaps the polarity back but the wiring to my extension reverses the polarity again. To cement this theory I plug the modem straight into the test socket on the master and it connects So I swap the wires on the master socket, screw it all back together, plug the modem in, and flashing DSL light on the modem / no connect

So I'm still none the wiser as to what the problem is. According to Google the Openreach modem doesn't care about polarity so probably been barking up the wrong tree there. Maybe the faceplate is broken, or does having the extension connected cause problems? I didn't think to try it last night but I'll try it without the extension attached tonight. Failing that I'll be connecting a really short extension from the master socket and using that.

Graz

In case anyone finds this thread in years to come it's working now, disconnected the extension and all good. Put the polarity back the right way on the master socket too.

I suspect that having an extension connected should be fine but it should only be for DSL and just terminated in a normal RJ11 socket. As I was using an existing extension it already had a filtered socket attached to it for ADSL. Plugging the Openreach modem into the ADSL connector on that worked fine but I suspect the filter was somehow interfering with the signal when I plugged the modem back into the master socket.

paul98typer

Glad its back working and can confirm that polarity makes no difference what so ever. And have been on faults where the modem has been moved back to the main nte with the extn left connected and it caused problems.

shooter007

To many filters across the line,dsl extns should be plugged into front of main socket and as you found no other filter at extn end sorry just seen this.