Happy but still puzzled

[tehidyman]

I posted this query on TBB forum with no solution. Can IDNetters solve this puzzle ?
My BT landline lost dialling tone on both DECT phone and corded phone on the extension and would not accept incoming calls. It was the same in the master socket (ADSL NTE5 filtered faceplate) and in the test socket. Infinity FTTC was unaffected running on the filtered extension (Cat5e cable from the unfiltered terminals on the back of faceplate)
BT online help wanted me to connect my Homehub 5 to the test socket and connect to the internet. This I did, and as forecast phones became fully functional. I am happy that it worked but puzzled as to how it could work . Suggestions appreciated.

[Technical Ben]

Have you put the other cabling back? It suggests your extension cables are at fault.

[tehidyman]

As soon as the phones started working in the test socket they were connected back as originally and continue to work fine.  A point I realise I have not made clear is that the  DECT phone that lost dialling tone was plugged into the master socket and when it lost dialing tone I tried the corded phone in the extension, then in the master and then both in the test socket. The BT help person was quite insistent that I should connect to the internet via the test socket as a next step in correcting the fault . Using the test socket had disconnected me from the internet.

[Gary]

It could be a battery fault on the line, or one leg of the pair is not connecting properly, although that generally effects your BB speed, have your provider run a line test to rule that out.

[Technical Ben]

Sounds similar to the ongoing problem at a friends. Phones crackle, internet stops working, and BT say "there is no fault". Gah! 

[tehidyman]

Had checked broadband speed and it was unaffected and was able to connect and download with no problem.  BT. ran a line test and reported no fault.

[nowster]

ADSL will happily continue if there is no DC path on the line, but there still is an AC path (eg. a tiny gap in continuity). Telephone usage needs a DC path to "sieze" the line, and signal to the exchange that the line is in use. The exchange then provides dial tone, etc. etc.

It could be a dry joint in the socket. Wiggling things round made things connect solidly again.

[Gary]

Its vary rare for a test socket on an NTE5 to go but no unheard of, but that would have shown up as a fault in the line test 

[nowster]

Its vary rare for a test socket on an NTE5 to go but no unheard of, but that would have shown up as a fault in the line test 

Actually, if the break occurs after the "out of service resistor" and surge arrestor, it would still test out OK from the exchange end.

[Gary]

Actually, if the break occurs after the "out of service resistor" and surge arrestor, it would still test out OK from the exchange end.

If its a VDSL faecplate there isn't a 'high' voltage surge arrestor as it causes issues with FTTC higher frequencies. The layout was changed a bit, there is still a surge arrestor but its not the same and the later faceplates also have a small REIN filter too, but if the faceplate breaks down it should show as a fault inside your home if its the test socket connection to the circuit board.

I had an old BT version one break down, which showed as a fault. Thats how the system is set up from what I believe, although I could be wrong. The out of service resistor is there to enable test without a phone being plugged in so if that fails the line should still show as failing the test I would have thought. The OP is saying he was plugged into the test socket, since that connects the faceplate when its on if that test socket has broken down it should show as a fault as there would be no dial tone surely? 

[nowster]

Nope. The "out of service" resistor is there to allow the exchange to test for continuity.

If the break is in the soldering of the internal socket's pins, ie. it doesn't disconnect the continuity path through the resistor, automated tests will show absolutely nothing wrong with the line.

[Gary]

Nope. The "out of service" resistor is there to allow the exchange to test for continuity.

If the break is in the soldering of the internal socket's pins, ie. it doesn't disconnect the continuity path through the resistor, automated tests will show absolutely nothing wrong with the line.

I queried this with my BT engineer friend, if the test socket fails you should have a line fault, and it should show within the premises, I take his word as he has been in the business over twenty years. As to the 'Out Of Service Resistor'

'The Master Socket has three components fitted that are not fitted in Secondary Sockets. These are a surge arrestor (really just a spark gap), a "bell" capacitor to provide the ringing to pin 3, and an "out of service" resistor. The resistor ensures that when the line is tested from the exchange, a resistive loop can be measured. When reporting a fault, this is one of the first tests carried out, often after the customer has been asked to unplug all their phones. If the resistor can be measured from the exchange (I think it is 470 kohms), this implies that the external cable section up to the master socket is intact. The resistor and capacitor are in series, so the line should test open-circuit with a dc test, and the resistor can be measured with an ac test. Between the Master and Secondary sockets, pins 2, 3 and 5 should be connected. Pin 4 is occasionally used as an earth, but not generally needed (and generally not connected). Pins 1 & 6 were marked as "future" in the original standard, and have never been defined. Additional resistors and capacitors may reduce the broadband speed available with ADSL' Therefore as I said the 'out of service resistor' is there to test without any phones connected. 

[nowster]

You're right. The wiring inside a BT master socket is like this...



Which obviously cannot prove there's a DC path from exchange to socket. Seizing the line (obtaining dial tone) requires a DC current to be drawn from the exchange, which won't be there if there's any break in continuity.