Power line adaptors - checking power sockets?

[#1]

Can anyone recommend a device I could use to test if a power socket in the house can carry a signal via a powerline adapter please? I've got a couple of TP-LINK TL-WPA4220KIT AV500's connected around the house, and happily giving out a clear and solid signal. Unfortunately there's one room in the house in which one of the sockets do not seem to be able to host AV500's. This happens to be the socket nearest the TV/Sky box, and the one I want to use. As far as I can see there's nothing different to this socket from any of the others in the house/room - infact the telly, skybox and everything else's been running off it happily for years. Can't understand why this socket out of all the others can't carry a signal?
If there is an easy way to check, via a device of some sort, then I'd be very grateful to know.
Many thanks.

[#2]

Are you testing in the socket ? or on an extension/gangway plugged into the socket ?

[#3]

One possibility - although it would be most unusual
Is that socket fed from the downstairs ring main or from a spur direct from the consumer unit or worse still a separate consumer unit

[#4]

Unscrew the brass screws holding the socket to the box.
Look at the wires (but do not touch).

[#5]

Thanks guys. It's a normal socket, against the skirting board - no extension or gangway. I'll happily look at the wiring, if someone can explain what I'm meant to be looking out for?
Many thanks again.

[#6]

I suggest you turn the power off at the consumer unit before looking.
Check it's red to live and black to neutral!

[#7]

Normally the units come with a CD which has utility software which gives the home plugs "seen" by the local one near the computer running the utility. Normally you can see the speeds being delivered as well.  
So the home plugs can be used to do the testing  

[#8]

Or, if it is a newer property
Brown to line and Blue to neutral

[#9]

Thanks Peter, but I think it's the wiring in the house that might have a problem. I want to eliminate or solve that first.
I've tried a safety socket tester - and it came up with 3 lights (meaning everything's "correct"). But still can't get a signal to the AV500's (the lights just remain solid, rather than the usual blinking). Wireless devices in the vicinity can see a signal coming from the AV500 in this socket, but definitely can't connect.
Opening up the socket was something I wanted to avoid (for obvious reasons), but I'll give it a go. Cheers! 

[#10]

And no insulation (probably) on the earth conductor.
I've seen sockets where the wires are loose, the insulation is made of rubber or cracked etc.
It should have plastic covered wires.
If it is part of a ring main, each wire going to a connection will be two wires twisted together.
If it is a spur, then only one wire into each connection.

[#11]

Thanks. But would 3 lights on a safety socket tester not indicate everything was performing correctly? Rather than opening it up?
Cheers.

[#12]

If you've checked with a tester and got three lights you've at least ruled out a L N swap.
Personally, I'd want to find out how the socket is fed.  
First, look at you consumer unit/fuse box - Does it have a row of toggle switches (MCBs) or fuses that you pull out?  
Are they labelled in a way that makes sense to you ie downstairs ring, upstairs ring, lighting etc?
Try plugging a lamp into a 'working' socket and the problem socket and then turn off the relevant ring MCB (or pull the fuse) - Do both lamps go out?

[#13]

Actually, one indication of the age of your socket is how close it is to the floor.
They keep changing the regulations!
It used to be common to put it about 1" above the floor - currently it's maybe 12" above the floor.

[#14]

Quote from: pwatson

If you've checked with a tester and got three lights you've at least ruled out a L N swap.

Does it also rule out a neutral/earth swap?

[#15]

Generally no, but if the socket is fed from an RCD it would trip.
Testing by isolating the circuits is most definitely the correct initial procedure, not delving into wiring at this stage!