HP t420 Troubleshooting Guide - Page 30

Power-On Diagnostic Tests, Interpreting POST Diagnostic Front Panel LEDs and Audible Codes

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Power-On Diagnostic Tests The Power-on diagnostics performs basic integrity tests of the hardware to determine its functionality and configuration. If a diagnostic test fails during hardware initialization the unit simply stops. There are no messages sent to video. NOTE: You may try to restart the unit and run through the diagnostic tests a second time to confirm the first shutdown. The following table lists the tests that are performed on the unit. Test Boot Block Checksum DRAM Serial Port Timer RTC CMOS battery NAND flash device Description Tests boot block code for proper checksum value Simple write/read pattern test of the first 640k of memory Tests the serial port using simple port verification test to determine if ports are present Tests timer interrupt by using polling method Tests integrity of RTC CMOS battery Tests for proper NAND flash device ID present Interpreting POST Diagnostic Front Panel LEDs and Audible Codes This section covers the front panel LED codes as well as the audible codes that may occur before or during POST that do not necessarily have an error code or text message associated with them. WARNING! When the computer is plugged into an AC power source, voltage is always applied to the system board. To reduce the risk of personal injury from electrical shock and/or hot surfaces, be sure to disconnect the power cord from the wall outlet and allow the internal system components to cool before touching. NOTE: Recommended actions in the following table are listed in the order in which they should be performed. Not all diagnostic lights and audible codes are available on all models. Table B-1 Diagnostic Front Panel LEDs and Audible Codes Activity Beeps Possible Cause Recommended Action White Power LED On. None Computer on. None White Power LED flashes every two seconds. None Computer in Suspend to RAM mode (some models only) or normal Suspend mode. None required. Press any key or move the mouse to wake the computer. Red Power LED flashes two 2 times, once every second, followed by a two second pause. Beeps stop after fifth iteration but LEDs continue until problem is solved. Processor thermal 1. Ensure that the computer air vents are not protection activated: blocked and the processor cooling fan is A fan may be blocked or not plugged in and running, if equipped. turning. 2. Contact an authorized reseller or service provider. OR 24 Appendix B Diagnostics and Troubleshooting

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Power-On Diagnostic Tests
The Power-on diagnostics performs basic integrity tests of the hardware to determine its functionality and
configuration.
If a diagnostic test fails during hardware initialization the unit simply stops. There are no
messages sent to video.
NOTE:
You may try to restart the unit and run through the diagnostic tests a second time to
confirm
the
first
shutdown.
The following table lists the tests that are performed on the unit.
Test
Description
Boot Block Checksum
Tests boot block code for proper checksum value
DRAM
Simple write/read pattern test of the
first
640k of memory
Serial Port
Tests the serial port using simple port
verification
test to determine if ports are present
Timer
Tests timer interrupt by using polling method
RTC CMOS battery
Tests integrity of RTC CMOS battery
NAND
flash
device
Tests for proper NAND
flash
device ID present
Interpreting POST Diagnostic Front Panel LEDs and
Audible Codes
This section covers the front panel LED codes as well as the audible codes that may occur before or during
POST that do not necessarily have an error code or text message associated with them.
WARNING!
When the computer is plugged into an AC power source, voltage is always applied to the system
board. To reduce the risk of personal injury from electrical shock and/or hot surfaces, be sure to disconnect
the power cord from the wall outlet and allow the internal system components to cool before touching.
NOTE:
Recommended actions in the following table are listed in the order in which they should be
performed.
Not all diagnostic lights and audible codes are available on all models.
Table B-1
Diagnostic Front Panel LEDs and Audible Codes
Activity
Beeps
Possible Cause
Recommended Action
White Power LED On.
None
Computer on.
None
White Power LED
flashes
every
two seconds.
None
Computer in Suspend to
RAM mode (some models
only) or normal Suspend
mode.
None required. Press any key or move the mouse to
wake the computer.
Red Power LED
flashes
two
times, once every second,
followed by a two second pause.
Beeps stop after
fifth
iteration
but LEDs continue until problem
is solved.
2
Processor thermal
protection activated:
A fan may be blocked or not
turning.
OR
1.
Ensure that the computer air vents are not
blocked and the processor cooling fan is
plugged in and running, if equipped.
2.
Contact an authorized reseller or service
provider.
24
Appendix B
Diagnostics and Troubleshooting