Asus TS300-E7/PS4 - Manual (Page 71)

ASUS TS300-E7/PS4 4-19
4.4 Internal 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.
2. BMC LED (BMC_LED1)
The green heartbeat LED blinks per second to indicate that the ASMB5 is
working normally.
The heartbeat LED functions only when you install the ASUS ASMB5.