Scart Connector Box

[bigbanana]

I'm experiencing problems connecting up some equipment to a TV via a scart connector box and I'd be grateful for some advice
I've recently bought a freesat box and run the cable myself to the dish using F plugs etc. The signal strength of the connection is around 80% and I've got a good picture and sound volume on the portable TV that the cable is connected to.
My son asked me if I could reconnect his X-box to the TV and with this in mind, I bought a simple, unswitched and unpowered Scart connection box like the one shown on the following link:

http://cgi.ebay.co.uk...0a0aad537ae87ffff817d

The X-box has a number of leads terminated in phono plugs. These phono plugs are connected to a Scart 3 phono plug adaptor unit which was formerly plugged into the TV Scart socket when needed. The problem I've found now is that if I plug the X-Box adaptor into the Scart connection box and plug the Scart flylead from the box into the TV, I get a hum on the picture and very reduced volume from the TV that cannot be increased by the TV or freesat remote controls. The volume is ok if I plug the Scart phono plug adaptor straight into the TV. The same thing happens if I plug a DVD player Scart lead into the Scart connection box, although I still had the X-Box connected via another socket on the Scart box at the time.
I'm now back to connecting up the X-Box and DVD when needed without using the Scart connection box which is annoying.
Can anyone explain what is going on here please? Would a switched, Scart connector box be any better? Does it have to be powered?

Thank you.