Brain Board (Raspberry Pi)¶

There are two LEDs on the Raspberry Pi itself: PWR and ACT. Both are located on the lower left side of the board.

The LEDs on the KCH can also provide indication as to the state of the Raspberry Pi.

Power LED (red)¶

The red PWR LED broadly indicates that there is 5V power to the Raspberry Pi.

Unlike other Raspberry Pi models, on a Raspberry Pi 4 the PWR LED is fully under the control of a GPIO expander, and when booting this IO expander is reset, causing the PWR LED to blink off on reboot. On booting the bootloader enables it again.

However, if the PWR LED goes off (blinks) at any other time it means have an unfit power supply/power cable.

In short, the PWR LED should be always on except for a very short time just before a reboot happens.

Activity LED (Green)¶

The green ACT LED will flash "randomly" during normal usage and indicates access to the SD card.

If the Pi fails to boot, the ACT LED should flash in a pattern. If the ACT LED does not turn on, even though the PWR LED does, this indicates that the EEPROM is corrupt. It may be fixed using the recovery.bin method, which can be performed using Raspberry Pi Imager.

The ACT LED patterns are listed in a table below, which was compiled from a variety of sources. The probable reasons have been written specifically for the runbook.