can't connect to 2.4g wifi - I have tried with multiple devices
5g OK and ethernet OK
I install old apple airport and 2.4g wifi works straight away
tried changing channels many times still nogo
Sounds like the device has developed a fault, try "factory resetting" the device and see if it comes back. If the 2.4ghz has not returned, then it's faulty.
If its within its warranty, Optus can replace it via contacting them to have it done.
If it's outside warranty, then Optus replacing it for free is at their discretion.
but I have new info,
Today I decided to try the router at my Dad's house, where it worked OK
So I think the router is OK,
but something is causing interference on the relevant frequencies in or near my house
my next course of action is to unplug every wifi device I have in my house and then re-test
If that works then plug back in every device until I find the culprit
If that doesn't work then the prob could be external, not sure what I would do in that case.