What device is the main router in the network??
When you say the other devices don't work.. exactly what do you mean and how do you know?
Please plug a computer directly into the bridged extreme by ethernet and get an ip address it is running.. did it pick up the IP correctly from the main router?
If it doesn't work via the switch, please plug it directly into the TC.. and ensure that the connectivity leds turn on, in both devices and also to the computer connected.
Note also for wireless to work properly you might need to fix the radio channels ..
So did you follow the apple instructions for roaming network?
I would just add to that, use the 3 wireless channels.. 1, 6, 11 which do not overlap.. set each one to one of those channels. Use the same wireless name, security setting and password.
Thanks for helping. The modem is a Huawei fiber modem, ethernet cable into the time which acts as the main router. It is in the hub room and I have Ethernet cable from one of the 4 lan ports at the back of the tm into the switch.
All computers connected by Ethernet have access to the Internet no problem. When I plug in an a extreme or express which is in range of the Tim wifi then it works fine and extends the range. If the extreme is outside the wifi range and/or I plug in an Ethernet cable then the extreme will not function or connect with the network, the light is yellow and I cannot see the device on airport utility.
I did as you suggested by plugging the extreme direct into the TC but the same problem so it seems it is not the switch problem. Checked channels, have the same ssid, security and password (as I say, wireless it works). I am pretty sure that I followed the apple instructions for roaming although the interface looks different (i am on mountain lion with the mac).
The TC is using 7.6.1, it is a few years old now.
Sent from my iPad