Faulty electronics between Test and Master BT socket?

Our internet speed often drops to 1/10th of what it is during the day. I can plug into the BT Master, and get the same results. However, if I plug into the BT Test socket, my speed is normal again. The results are the same regardless of whether any extensions are connected or not. Yes, I've switched ADSL filters and routers and RJ-11 cables and pretty much everything else, including testing in Windows Safe Mode. In BT's speed tests, I even got a downstream connection speed of 0 once! Typical night speed from Master socket is 330 Kbps (but variable). Typical day speed without any other changes is 3300 Kbps.

Thoughts?

ISP: Zen Internet
OS: Windows XP SP3
Router: Currently Belkin N Wireless; also with Netgear DG834G (v3)
Connected to the Test socket:
Attenuation (down/up): 65/29
SNR (down/up): 7/7
Datarate (down/up): 3668 / 792 Kbps

We need to see the stats from the normal socket when it's bad, then from the test socket straight after, then from the normal again straight after that.

Sky box not filtered?

It is possible the contacts on the faceplate are bad, easiest thing might be to get a filtered faceplate to replace the current one.

How would that account for it being OK during the day?

Perhaps I read it wrong but it looked to me like everything is OK without the faceplate but the problem is only present with the faceplate fitted, with or without extensions.

Definitely night-time only. But still OK in the test socket. Which to me suggests something affecting the ring wire, or an unfiltered/dead filter night-use device.

[cue] . Therefore your solution would probably work. [/cue]

If that 65db downstream attenuation is correct Bob, then an unfiltered Sky box is going to give you a serious case of no sync.

In reply to a post by RobertoS:

We need to see the stats from the normal socket when it's bad, then from the test socket straight after, then from the normal again straight after that.

Sky box not filtered?

I'll try to get those stats to you, but probably won't be this weekend. Couldn't sleep so I'm up now, but of course it won't misbehave when I want it to!

No, we have no Sky box. The layout is:
[TEST socket -> MASTER socket] -> extension -> DSL filter
->> Belkin router (ADSL side of filter)
->> telephone (phone side of filter)

The problem occurs equally without the extension and without the telephone connected to the filter.

In reply to a post by Going_Digital:

Perhaps I read it wrong but it looked to me like everything is OK without the faceplate but the problem is only present with the faceplate fitted, with or without extensions.

True, but it's always OK during the day even with the faceplate fitted, and acts up intermittently at night.

Is the router near to something like a TV or other electronics? I gather you are getting actual disconnections and low reconnection speeds, not just throughput.

Does the line come in from a pole outside, or underground? If from a pole, does it go near a street light? Or any security lighting?

Edited by RobertoS (Sat 10-Mar-12 10:01:57)