The following information is specific to the Raspberry Pi Model 4, which has an entirely new boot flow relative to previous Pi models. Boot code is now located on a built in boot EEPROM - NOT on the SD card. Older models used a boot.bin file located on the SD card.
This is a simple sanity check of the Pi's state.
- Remove power.
- Remove everything connected to Pi.
- Remove SD card.
- Apply power.
If the EEPROM bootloader is working correctly, you should see a repeating pattern of 4 blinks on the green LED. This is the warning code that indicates "start*.elf not found", which is expected since the SD card that contains that file has been removed.
If the expected blink pattern did not appear, then it may be a corrupt EEPROM bootloader image. The following is how to attempt a recovery to re-image the EEPROM bootloader code.
To attempt a recovery repair of the EEPROM bootloader, a special recovery SD card image is used. This can be created using the rpi-imager software tool.
Install the SD card into the computer running rpi-imager.
Now that the recovery SD image has been created, do the following on the Pi 4 to attempt bootloader image recovery.