Yealink SIP-T48G Administrator's Manual page 260

Microsoft Lync Edition Administrator's Guide for SIP-T2_Series and T4_Series IP Phones
Do one of the following:
Ensure that the IP phone is properly plugged into a functional AC outlet.

Ensure that the IP phone is plugged into a socket controlled by a switch that is on.

If the IP phone is plugged into a power strip, try plugging it directly into a wall

outlet.
If your phone is PoE powered, ensure that you are using a PoE-compliant switch or

hub.
'
Do one of the following:
Ensure that the Ethernet cable is plugged into the Internet port on the IP phone and

the Ethernet cable is not loose.
Ensure that the Ethernet cable is not damaged.

Ensure that the IP address and related network parameters are set correctly.

Ensure that your network switch or hub is operational.

Press the OK key when the IP phone is idle to check the basic information (e.g., IP
address, MAC address and firmware version).
'
Do one of the following:
Ensure that the target firmware is not the same as the current firmware.

Ensure that the target firmware is applicable to the IP phone model.

Ensure that the current or the target firmware is not protected.

Ensure that the power is on and the network is available in the process of

upgrading.
Ensure that the web browser is not closed or refreshed when upgrading firmware

via web user interface.
Ensure that the target firmware on the Lync server is available.

248