How to verify whether there is a hardware issue of TP-Link DSL Modem Router

Note: Please check the light status according to the Quick Installation Guide at first.

Below we list some common problems you may encounter.

No LED on at all

Confirm whether you have enabled LED control function ( Not all the DSL Modem Router support this feature)
Change another outlet to plug it
Hold the reset button/hole to hard reset it according to the QIG
Ensure that it is the original power adapter
Change another power adapter also

Conclusion: There is still no LED light on, please email TP-Link Technical Support with the model number, serial number, hardware version and proof of purchase to get a replacement.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support

DSL led does not come on or it is flashing

Ensure that there is a phone line provided by ISP to get internet, not an Ethernet cable and ensure that it is plugged into the DSL port
Remove the splitter
Change another phone line
Reset the DSL modem router by holding the reset button/hole per QIG
Contact the ISP to check the line quality or change another modem to do a comparison analysis.

Conclusion: If the DSL led is still off or flashing, please email TP-Link Technical Support with the model number, serial number, hardware version and proof of purchase to get a replacement.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support

Wireless led does not come on

Ensure wifi button/switch is turned on if there is one
Login to the web interface to confirm that the wireless function is enabled
Hold the reset button/hole to hard reset it according to the QIG

Conclusion: There is still no wireless led on, please email TP-Link Technical Support with the model number, serial number, hardware version and proof of purchase to get a replacement.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support

Ethernet led does not come on

Ensure that there is a device connected to the Ethernet ports
Change another Ethernet cable
Change another wired device

Conclusion: Still the same, please email TP-Link Technical Support with the model number, serial number, hardware version and proof of purchase to get a replacement.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support

All the LEDs are flashing, including the power led, while after a while, all the LEDs will go off and then the power light come on and the rest of lights come on gradually.

Confirm whether you updated the firmware recently or not and how
Reset the DSL modem router by holding the reset button/hole as the QIG
Do a firmware recovery if the DSL modem router supports this feature (You can contact TP-Link technical support to verify it)

Conclusion: If it cannot be fixed, please email TP-Link Technical Support with the model number, serial number, hardware version and proof of purchase to get a replacement.

https://www.tp-link.com/support/contact-technical-support/#E-mail-Support