Identify The Issue; Understand The Issue; Boot Up Sequence; Failure Classification - HP EliteBook 850 G4 Maintenance And Service Manual

Identify the issue

1. Understand the issue

It is important to understand the issue that occurred, including related symptoms. It helps to understand the
basic computer boot-up sequence as well as the failure itself. The boot-up sequence and associated failures
are described below.

Boot up sequence

The computer performs several steps after you press the power button or restart the computer.
It is important to understand where in the boot-up sequence the symptoms occur. The following table lists
the phases of the boot-up sequence and explains the symptoms that may occur in each phase. For example, a
blue screen error (BSOD) often occurs during the performance phase.
Table 8-2 Boot-up sequence
Power-on
POST (UEFI/BIOS)
Performance
(operating system)

Failure classification

Failure classification is a breakdown of different types of failures and symptoms that could occur during the
boot-up sequence. Table 3 and table 4 represent the failure classification for common notebook failures.
Table 3 categorizes failures by the boot-up sequence.
1. Power-on: Common issues are No Power, Recycle/Reboot, etc.
2. POST: Common issues are No Boot (have power), Light Flash or Diagnostics Error.
3. Performance: Common issues are Intermittent Loss of Power, Blue Screen, Hang, etc. In many cases,
issues may be identified and associated with a particular hardware (i.e., display, storage).
Table 4 categorizes failures by hardware.
4. Display
5. I/O devices (Input/Output)
6. Storage
7. Mechanical
84 Chapter 8 Troubleshooting guide
After power button is pressed, the computer boots after all internal power rails (i.e., 5V, 3.3V) are stable.
Confirm that power lights are on fan is spinning.
Next step: If the computer experiences a power-on issue, see "Verify Power Good (Troubleshooting) lights" in
No Power on page 101.
Common issues: all lights are off; troubleshooting lights are on; does not boot; video is absent.
Power-On Self-Test (POST) verifies that hardware components (processor, hard drive, memory, etc.) are
functional. When POST is complete, the HP logo displays briefly and then disappears.
If there are errors, the computer may exhibit blinking lights and POST error messages
Common issues: lights blink, error message appears, hangs.
System boots to operating system, and Windows logo screen appears..
Common issues: hangs (lock up/freezes), blue screen, video distorted, driver conflict, slow performance,
display issue (dead pixel), I/O issue (no speaker sound), wireless/audio unavailable, noise.
See Analyze the issue on page 87 table below for detailed troubleshooting information).