This article aims to resolve issues where the phone is using Power over Ethernet but the display is blank and with no light indicator. When using PoE, the ethernet cable transmits the data and power simultaneously from a PoE compatible and compliant router or switch to your desk phone.
Scenario
• The IP phone does not boot up successfully.
• IP phone led light indicator is not lit.
• The IP phone screen is not displaying anything.
Environment
Polycom desk phone
Cisco desk phone
Yealink desk phone
Issue
Whenever the IP phone is plugged in to the router, the device fails to boot up the firmware causing it to display nothing on the screen or on the led light indicator.
Cause
Power failure for IP phones may be caused by the following.
• The IP phone is using a bad ethernet cable.
• The IP phone is plugged in to a bad port of a router/modem.
• The firmware of the IP phone may be broken.
Resolution
Most IP phones are using ethernet cables to power the desk phone.
• A PoE compatible and compliant Switch or Router is required.
• When a desk phone has a power adapter plugged in, it will not attempt to get power from the Ethernet cable.
• When a desk phone has only an Ethernet cable plugged in, it will attempt to get power from the Ethernet cable.
• Desk phones are auto-configured to use the correct power level using 802.3af, which all unmanaged & managed switches support by default.
Follow the steps below to isolate the issue.
1. Make sure to use a working ethernet cable.
2. Make sure that the ethernet cable is securely plugged in to the LAN port at the back of phone.
3. Make sure to plug the other end of the ethernet cable into a working ethernet port on a router/switch.
4. Plug the phone to a known good port on the PoE Router/Switch (preferably a port which has a device connected to it that is powered on by the PoE source, to make sure the port is working).
5. Use another ethernet cable.
6. Plug an AC power adapter to the phone. If the phone turns on using AC power, contact your local IT to fix your network. If the phone does not turn on using AC power, then the phone needs to be replaced.