Test socket problems and low speed

[#1]

I have an fault ticket open now for four weeks and increasingly frustrated by the slow responses from Plusnet's support agents.  In an effort to hurry things along, I would like to ask the collective for any views on the following issue.  When I plug my router into the BT test socket behind the face plate, as instructed to do, I find that my router does not complete the training period and synchronise with the exchange.  When plugged into the normal socket, the router synchronises, but at half the line speed I was seeing 5 weeks ago (hence the fault report). So possiby my internal wiring is actually completing a connection which is faulty on the BT line?
The loss  in line speed occurred after I experienced a telephone fault (no dial tone) which was subsequently fixed by BT.  I am convinced that there is a fault remainingg on the line which is causing the low ADSL speed.  However, with responses from the network team taking 48 hours or more, I am beginning to despair that they are capable of sorting out this fault.  Any ideas?

[#2]

I cannot account for your strange test socket issues but if your bad line caused frequent router disconnections then it may be that your target signal to noise ratio ("noise margin") has been raised with consequent loss of speed.  That is exactly what happened to me after I had a bad line/no dial tone caused by a wet and corroded connection.  You can find out what your SNR is by looking at the figures your router reports.
If that is what has happened then it should correct itself if you wait long enough (it's a very long wait) but Plusnet can accelerate the process by setting your line to retrain.   

[#3]

Thanks for the response.  Router (Thomson 585v7) reports S/N Margin (up/down) [db] 10.0/7.5.  Don't know whether these are raised figures.  Also tried a D-link DSL-604 (which I thought was good) on the test socket, but I waited an hour for that to synchronise and then gave up.

[#4]

The target downstream SNR (which is what counts for your broadband speed) is 6 dB.  7.5 dB is close enough to 6 dB that it's probably the right value, it get increased in 3 dB increments if your line is perceived as unstable.  So what does your router say your downstream sync rate is?  And if you run a speed test at http://speedtester.bt.com/ , what is your IP Profile?

[#5]

BT speedtest site gives the followiing: 
1732kbps download speed
DSL rate 3392kbps down, 448kbps up
IP Profile 2000kbps
5 weeks ago the IP profile was 4500kbps

[#6]

Hi donne,
I've one of the faults team picking this up for you now.
Jojo

[#7]

I hope this issue has now been resolved following a visit from the BT engineer.  He told me that the problem was underground outside in the road - apparently my line was wired up with a 'split core'.  This, he said, is OK for telephony but rubbish for broadband since the bandwidth is much reduced, although not showing up on any of the remote testing carried out by Plusnet or BT.  Incidentally, the engineer's own test equipment failed to synchronise with the exchange equipment on the test socket although working on my wiring - presumably in some way my wiring was loading the BT line such that a connection could be established.  This confirms my own experience with a router connected direclty to the test socket which similarly failed to synchronise as I noted above.  A recent BT speedtest shows a DSL connection rate of 6432kbps and a IP profile of 6500kbps - increased by a factor of 3 times. 
I am pleased with this result although taking nearly 6 weeks from raising a ticket with Plusnet.  One wonders how many thousands of other broadband customers out there suffer unknowingly a degraded broadband service through duff BT wiring.