To recover a bricked router, you can try several specific methods. First, perform a hard reset by pressing and holding the reset button for about 10 seconds while the router is powered on. If this doesn't work, attempt to access recovery mode, which varies by manufacturer. For example, many Linksys routers allow access to a firmware recovery mode by holding the reset button while powering on the device. Additionally, if the router supports TFTP, you can upload the original firmware using a TFTP client. Ensure to use the correct IP address as per the model, often 192.168.1.1.

To determine the integrity of the bootloader, connect the router to a serial console via a UART interface. If the bootloader is functional, you should see output during the boot process. You can issue commands to interact with the bootloader; for instance, you might type 'printenv' to check environment variables. If you receive no output or the boot process halts consistently, the bootloader may be corrupted. In this case, you might need to restore it via JTAG, which involves connecting a JTAG programmer to the appropriate pins on the router's PCB.

A failed firmware update can potentially corrupt the flash memory or disrupt the system's RAM functionality. To diagnose, start by measuring the voltage levels across the flash memory chip (usually found on the PCB labeled as NAND or NOR flash). Use a multimeter to check if the chip receives proper voltage. Additionally, inspect for short circuits or visible damage on the PCB. For deeper diagnosis, you may need an oscilloscope to monitor data signals during the boot process, validating proper communications between the CPU and flash memory.

To recover a router running custom firmware back to the original manufacturer firmware, first, use a TFTP client to upload the stock firmware. Ensure you have the correct firmware file specific to your router model. Connect your PC to the router via an Ethernet cable and set your PC’s IP to a static address in the router's default subnet (often something like 192.168.1.2). Power on the router while initiating the TFTP transfer. Some routers may require you to hold the reset button during power-up to enter recovery mode for TFTP uploads.

If your router is partially operational, you may access log files through a console connection. If the router supports serial output, connect a serial cable and use terminal software to capture boot logs during startup. Look for error messages indicating failed memory checks or unexpected exceptions. If available, checking the bootloader's debugging output can also provide critical insights. If logs aren't accessible because the router is completely unresponsive, consider checking for failed checksum validations in the firmware image that may indicate corruption or incomplete uploads.