Dell T7500 service manual Diagnostic Light Codes, Pre-POST Diagnostic Light Patterns

	the power supply is fine. Look at the diagnostic lights for further information.
Blinking
Green	System is in a low power state, either S1 or S3. Look at the diagnostic lights to determine which state the
	system is in.
Solid
Green	System is in S0 state, the normal power state of a functioning machine.
	The BIOS will turn the light to this state to indicate it has started fetching opcodes.

Diagnostic Light Codes

Four (4) single color lights are incorporated on the front control panel to serve as a diagnostic aid for troubleshooting systems exhibiting No Post/No Video symptoms. The lights do NOT report runtime errors.

Each light has two possible states of OFF or ON. The most significant bit is labeled with the number 1, and the other three are labeled 2, 3, and 4, as you go down or across the LED stack. The normal operating condition after POST is for all four lights to be ON and then turn off as the BIOS hands over control to the operating system.

Pre-POST Diagnostic Light Patterns

State

Pb0a

Pb0b

Pb0c

Pb1

Pb2

Pb3

Pb4

Pb5

Light Pattern	Light	Power	State
( 1 2 3 4 )	Description	Light	Assignment
	1- Off		System
	2- Off
	3- Off		Unplugged
	4- Off
	1- Off		ACPI S0;
	2- Off
			Normal
	3- Off
			Operation
	4- Off
	1- Off
	2- Off		ACPI S1
	3- Off
	4- Off
	1- Off		ACPI S4 or
	2- Off
	3- Off		S5
	4- Off
	1- Off
	2- Off	-	Reserved
	3- Solid
	4- Off
	1- Off
	2- Off		ACPI S3
	3- Solid
	4- Solid
	1- Off
	2- Green	-	Reserved
	3- Off
	4- Off
	1- Off
	2- Green	-	Reserved
	3- Off
	4- Green

State Description

System is not plugged into AC, PSU is not plugged into system board, or control panel not connected to system board.

System is on with no failures detected. This is actually a BIOS controlled state and is also S0e.

Windows Standby State.

Hibernate or Soft off. System plugged in, but either turned off or in Windows Hibernation State.

Reserved

Suspend to RAM Windows Standby State.

Reserved

Reserved