AP50 no 5ghz channels

Hi,
I have an AP 50 which quite happily works on the 2.4ghz band, blue light on etc. The 5ghz band, no blue light.
In the same room as the AP50 are 3 5ghz phones.
I have checked the configuration and it shows 5ghz active, 100% and 4 channels available. It is assigned an SSID which works with the 2.4ghz band.
The log doesn't show anything obvious to me.
:)
Any ideas?

Thank you

Ian