Given that the OP described the outermost connection as being "lozenge-shaped" (Fri 06-May-16 19:43:41), could it be one of the much-older screw-type "boxes" or termination units, given that it appears to be over 33 years old?

" it's a very old installation with the BT wires arriving at a lozenge shaped junction box"

I would then be suspicious of the screws having slackened slightly and/or corrosion, given the photo/s displayed on another thread recently.

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As you have requested, he really needs to sketch the present arrangement, with photos or descriptions of each connection, to help clarify the present situation.

Blimey, missed that. OK I'll shift the piano and unscrew the first socket and draw it up. Something I think is correct is obviously wrong so that is a good idea. Will show filters too.

Yes it's an old installation. Thinking back, the line upstairs used to end in one of those old junction boxes that we used to have screwed to a window sill which was hard wired to a phone. I took that out and put in the modern adslnation filtered box years back. The first one eventually failed so the current one is a replacement.

Edited by MrOptimistic (Fri 20-May-16 16:40:10)

In reply to a post by MrOptimistic:

Thinking back, the line upstairs used to end in one of those old junction boxes that we used to have screwed to a window sill which was hard wired to a phone. I took that out and put in the modern adslnation filtered box years back. The first one eventually failed so the current one is a replacement.

We need a layout diagram as well please. And preferably photos of the insides of every socket there is. Otherwise there could be a week of questions and none of us would be certain even then.

If you do resort to a sketch, indicate the type of NTE or other "junction box" used at each joint.

Your mention of "Piano" rang bells from a tale of over half-a-century back.

A colleague had trained as a Post Office Telephone Boy, graduating in to adult service.

One day, his manager asked him to go to a house where one of those rarities, a (land-line) telephone had been installed - just that very day.

The customer had phoned to report a problem; but was almost hysterical and the manager had not been able to comprehend what was the cause, particularly as the customer was using that very phone to complain - and thus it was clearly working.

My colleague jumped in his "glass-house" van of the period, and drove to the location.

As he approached the front door, he noted that the external wiring all looked fine to the two insulators of that era, then the cable came down the wall tidily to the top of the skirting board in the vestibule.

On being admitted, he followed the cable part way in to the hall-way, through a doorway in to the front room, along the the top of the respective skirting boards, to a wall, where the terminating block of the period was mounted, with the new phone on a small table.

Then he suddenly realised that the "wall" was actually the end face of the piano.

It's not that bad. I hope. Issues at work and prob 2 weeks in USA may delay things. I'll dismantle the boxes and see if I can describe the arrangement and identity the box type. Photos might be difficult.

However might have found an issue. The master socket has one input. The line upstairs to the modem goes from inside the socket, unfiltered. There are no other connection internally. However plugging in to the socket are three inputs. Physically these are in to a doubler socket which also has a fixed line from it. The inputs are two phones and the sky box. The doubler socket then plugs into a filter then in to the master socket. So three things hang off the filter.

Doesn't sound like best practice.......

Trouble is I have no way of knowing if separating all lines to give each a filter will cure the issue as until open reach change something there isn't any fault. Pretty sure I unplugged everything bar the old fashioned phone last time but can't honestly say I am sure. Do you think that may be it?

Even with this arrangement the line is very good for a long rural line. 54db attenuation downstream, and margin 9db. Rate 4143 kb. The router is throttled back with and tweak to reduce the rate. Left to its own devices it goes for 3db and a rate in mid 5000's which I reckon is pushing it a bit.

Sky boxes can sometimes need double filtering, particularly older types. So try Sky box into a dangly filter into the doubler. Leave the phone on the other doubler socket where it is, not into the new dangly.

Has the current filter ever been replaced?

"
The master socket has one input. The line upstairs to the modem goes from inside the socket, unfiltered. There are no other connection internally. However plugging in to the socket are three inputs. Physically these are in to a doubler socket which also has a fixed line from it. The inputs are two phones and the sky box. The doubler socket then plugs into a filter then in to the master socket. So three things hang off the filter.
"
Keeping in mind that the Modem/Router should have for its own purposes, a "straight-through" electrical connection with the incoming phone line, you appear to have that correct condition in that extension.

I'm not quite sure of the other connections, ie the doubler socket etc.

If these are "separated" from the incoming BT line by either one filter close to or in the master socket; or by individual filters in each of the onward three lines, picking up on the "PHONE" socket of a typical dongle, that should be OK; aside from total loading, given your long line.

In particular, the "fixed line" from the "doubler" might not be filtered.

Generally, make sure that all of the connections, whether by screws or plugs/sockets, doubler/dongles, are clean, bright and tight.

Oh, that might be that theory shot then. No idea where I got the doubler thingy from. It's like a standard doubler, but in addition has a built in line coming out if it which now goes to a phone. The doubler plugs into the dangle filter which then plugs into the phone box. So all three lines go through one filter. Of course eventually all lines are brought into a parallel connection when they get to the master socket, however with the current arrangement they are connected in parallel before the filter and not after it. That was what I wondered may be an issue.

I recognise that type of doubler, with an extension starting coming out of the doubler, almost as though the doubler is a tripler.

Remember to ensure that all the various connections are clean and bright.

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Most will probably have gold plating; and that can give rise to gold crystals, called dendrites, particularly when DC currents are present.

Most solid crystals are poor/non-conductors, so gradually the connection/s deteriorate, so should be opened/closed occasionally, say once per year.

Opening and closing breaks down the dendrites, effectively smearing them back to conducting gold.

http://www.te.com/documentation/whitepapers/pdf/p313...
"
Introduction

Metallic electromigration has long been recognized
as a significant potential failure mode in
many electrical and electronic systems
"