Asus TS300-E8-RS4-C - Manual (Page 64)

Chapter 4: Motherboard information 4-8
2. Baseboard Management Controller LED (BMC_LED1)
The green heartbeat LED blinks per second to indicate that the ASMB7 is
working normally.
The heartbeat LED functions only when you install the ASUS ASMB7.
4.3 Onboard LEDs
1. Standby Power LED (SB_PWR1)
The motherboard comes with a standby power LED. The green LED 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.