Dell Precision T7500 (Early 2009) - Manual (Page 12)

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
Light Pattern
( 1 2 3 4 )
Light
Description
Power
Light
State
Assignment
State Description
Pb0a
1- Off
2- Off
3- Off
4- Off
System
Unplugged
System is not plugged into AC, PSU is not plugged into
system board, or control panel not connected to
system board.
Pb0b
1- Off
2- Off
3- Off
4- Off
ACPI S0;
Normal
Operation
System is on with no failures detected. This is actually
a BIOS controlled state and is also S0e.
Pb0c
1- Off
2- Off
3- Off
4- Off
ACPI S1 Windows Standby State.
Pb1
1- Off
2- Off
3- Off
4- Off
ACPI S4 or
S5
Hibernate or Soft off. System plugged in, but either
turned off or in Windows Hibernation State.
Pb2
1- Off
2- Off
3- Solid
4- Off
- Reserved Reserved
Pb3
1- Off
2- Off
3- Solid
4- Solid
ACPI S3 Suspend to RAM Windows Standby State.
Pb4
1- Off
2- Green
3- Off
4- Off
- Reserved Reserved
Pb5
1- Off
2- Green
3- Off
4- Green
- Reserved Reserved