Compaq 486 Maintenance And Service Manual page 7

Chapter 2. Power On Self Test (POST)
Introduction
This chapter lists the subassemblies checked by the Power On Self Test (POST)
and briefly describes the types of error codes that can occur.
also includes problem isolation procedures and a flowchart for quick
reference.
Chapter 2.1 POST
POST is a series of diagnostic tests that runs automatically on the COMPAQ
PORTABLE 486c Personal Computer when it is turned on.
POST checks the following subassemblies to ensure that the computer system is
functioning properly:
o Processor Board
o Memory Module
o Keyboard
o Controller Circuitry
o Video Circuitry
o Fixed Disk Drive
o Diskette Drive
If POST finds an error in the computer, an error condition is indicated by an
audible and/or visual message.
for an explanation of the error codes and a recommended course of action.
Chapter 2.2 Preliminary Steps
If you encounter an error condition, complete the following steps before
starting the problem isolation procedures:
1. Turn off power to the computer.
2. Disconnect any external devices.
want to test the printer or use it to log error messages.
3. Install all appropriate loopback plugs and terminating plugs for complete
testing.
4. Clear the power on password, if it is preset by the user.
that the power on password is set when a key icon (0--m) appears on the
screen when POST completes.
to continue.
If you do not have access to the password, you must disable the power on
password feature by setting the power on password switch (see section
2.3, "Clearing Power on Password").
See Chapter 3, "Error Messages and Codes,"
Do not disconnect the printer if you
If this occurs, you must enter the password
The chapter
You will know