Asus Z87-A - Manual (Page 38)

ASUS Z87-A 1-28
3. POST State LEDs
The POST State LEDs provide the status of these key components during POST
(Power-On-Self Test): CPU, memory modules, VGA card, and hard disk drives. If an
error is found, the critical component’s LED stays lit up until the problem is solved.
2. TPU LED
The TPU LED lights up when the TPU switch is enabled.