AAEON EMB-KB1 - Manual (Page 19)

2-11 Chapter 2: Motherboard information
SB_PWR_LED1
ON
Standby Power Powered Off
OFF ON
Main Power Main Power Off
OFF
EMB-KB1 Onboard LEDs
MAIN_PWR_LED1
1. Standby Power LED
The motherboard comes with a standby power LED that lights up to indicate
that the system is ON, in sleep mode, or in soft-off mode. This is a reminder
that you should shut down the system and unplug the power cable before
removing or plugging in any motherboard component. The illustration below
shows the location of the onboard LED.
2.7 Onboard LEDs