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How to tell if an IP phone is defective

Posted by Daniel Noworatzky on Apr 29, 2020 10:49:00 AM

woman with a broken phone

While it doesn’t happen often, every once in a while you’ll come across an IP phone that simply won’t cooperate. You may have gone through every troubleshooting procedure that you can think of, but the phone continues to refuse to function correctly. You begin to consider the possibility of a defective phone, but before you invoke the manufacturer’s warranty, you want to be sure. Here we review the steps you can take to confirm, to a reasonably high degree, that the problem is indeed a defective device.

Manufacturers’ warranties

Most IP phone manufacturers sell their devices with a limited-time warranty of one or two years, whereby they will replace defective equipment at no cost. However, there are usually some stipulations that must be met, such as:

  • It has to be proven that there is indeed a defect with the device itself, and that the problem is not due to other factors such as configuration errors or network malfunctions
  • The defect must not be due to normal wear and tear, or because of rougher than normal usage of the device
  • Unless identified at the time of unboxing, physical defects that result from mechanical stress on the device, such as broken screens, damaged wires, or a cracked base are almost never covered

As you can see, not all defects will be covered, but it never hurts to express to the vendor exactly what you find. Warranties are honored more readily by manufacturers if the defects are found out of the box, while those that appear later within the warranty time period may be somewhat more difficult to unequivocally prove. In any case, it’s always a good idea to be completely honest with your vendor. You might find them respecting your integrity and replacing hardware that, strictly based on their policies, would not have otherwise been exchanged.

Common hardware problems on IP phones

Below you will find a description of the most common types of defects that may be found on an IP phone, either out of the box, or after a period of usage. If you encounter such behavior, follow the steps described, and if you intend to make a claim for a vendor’s warranty, keep a record of your observations, including both a written report, as well as photos, where applicable.


Issues involving power usually manifest themselves as a phone that simply doesn’t function at all when plugged in. In some cases, you may find a phone flickering on and off, as if the power is intermittent or is not quite enough for the phone to function properly. Phones will either obtain their power via Power over Ethernet (PoE) or through a separate power supply that plugs into a mains power socket. Some things to look at when this occurs include:

  • Attempt to power the device via both PoE and by a power adaptor (not at the same time) to see if the same behavior is observed for both power sources.

  • PoE comes in two types: non-standardized passive, and IEEE standardized (e.g. IEEE 802.3af); ensure that you are using the correct PoE source type for your device; otherwise you may irreversibly damage the electronics of the phone.

  • For PoE implementations that are not functioning, do the following:
    • Test the phone by connecting it directly with the PoE source device (switch, injector), and not via the structured cabling.
    • Ensure the source of the PoE is functioning correctly, whether it is a PoE switch or an injector. Attempt to plug the phone into a switch port or an injector that you know is working properly for another phone.
    • Try using a different Ethernet cable to connect the phone to determine if the cable is faulty.
    • Take a look at the pins of the Ethernet port on which the phone receives power. The pins should not be bent and should all be parallel to one another.

  • For a malfunctioning IP phone powered directly from the mains power supply:
    • Ensure that the power supply you are using is of the correct type.
    • Attempt to use another power supply from a phone that you know is functioning correctly.


Problems with IP phone firmware may be a result of corrupted memory, corrupted firmware files, or an incorrect firmware type being loaded into the phone. The symptoms of such problems can be almost anything, including a completely non-functional phone, to a device that displays unpredictable behavior. Because of the difficulty of identifying such a problem from the exhibited symptoms, it’s always a good idea, even as a last resort, to reset the phone to factory settings and load the manufacturer’s most up to date firmware. Even if the newest firmware is already installed, a reinstallation should still be executed as part of a standard troubleshooting procedure.

Firmware updates are usually implemented automatically “over the wire” when IP phones are registered to an IP PBX of the same manufacturer. Even so, it is a good idea to manually reinstall firmware on any phone that is suspected of having faulty firmware. Virtually all vendors publish the process by which firmware can be updated on their devices, and they make the required files freely available online. Download the newest version and follow the manufacturer’s update instructions.

Caution: It is important to ensure that the correct firmware is being installed and that the correct procedure is followed. If not, there is a risk of permanently damaging the phone. Needless to say, such damage is not covered by any manufacturer’s warranty.

If a factory reset and a firmware upgrade don’t solve the problem, attempt to install a previous firmware version as a last resort, since newly published firmware may sometimes, although rarely, still contain bugs.

Physical defects

Physical defects on the IP phone itself can be identified with a simple visual examination of the phone as well as an initial test of all of its functions. In most cases, they will be covered by warranties only if they have been discovered upon unboxing the device. Most physical defects that appear within the warranty period are difficult to claim for warranty purposes because it is tough to prove that they are due to faulty equipment, and not due to normal usage.

Some of the most common physical defects that you should look for include:

  • Screen problems – Malfunctions of the screen of an IP phone can manifest themselves in any of the following ways:
    • No image on the screen at all, even though the phone itself functions
    • Permanent horizontal or vertical lines on the screen
    • Dark blotches of burnt-out pixels are visible in various areas
    • Hot or dark pixels appear (pixels that are much brighter or darker than they should be, that do not conform to the image shown on the screen at that time)

  • Button problems – Moving parts on any device are often the most prone to damage. The buttons found on IP phones are no exception. Sometimes, the button mechanism will fail on a device, and this may or may not be covered by the vendor’s warranty, depending upon when the defect is discovered. Buttons should be physically inspected and manually tested during the initial installation of the phone.

  • Wires and handset – Other parts of the IP phone that experience mechanical stress are the handset, the spiral cord, and the network cable. These are components that should also be examined for physical defects out of the box, as well as within the warranty period. If you experience audio issues, test both the handset and the speakerphone. If you have another phone of the same model, try trading the handset and cord with a working phone to rule out the handset and cord as the defective culprit. Although these are not usually covered, because they are relatively cheap components, vendors may give you extra replacement cables or handsets if you have a good business relationship with them.

Failure in the electronic circuity

Defects in the electronic circuity of an IP phone are another type of failure that is difficult to detect. In fact, there is no way to determine such faults without opening up the device and using specialized measuring equipment to identify the problem. Doing this will void any warranty that you may have. If, however, the device is no longer covered, you may want to open it up and take a look, if just for educational purposes. Some of the telltale signs of failures in the electronics include:

  • Corrosion on the circuit board because of humidity, either due to spilled liquids (coffee?) or a humid environment
  • Disconnected solder joints at the base of electronic components such as capacitors or memory chips
  • Short circuits, indicated with a discoloration on the circuit board


Whether for the purpose of invoking a manufacturer’s warranty or to simply identify the source of a malfunction, it is not always easy to recognize problems that are due to faulty IP telephone hardware. Hopefully the tips provided here will help you determine whether a device is defective, as quickly and efficiently as possible.

You may also like:

How to fix IP phone registration issues

Putting the fun back into SIP phone provisioning

Equipping employees to use their enterprise IP phones at home


Topics: SIP Phones, Troubleshooting

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