UPGRADING REPAIRING PCs

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Chapter 3—BIOS Configurations and Upgrades
Reading BIOS Error Codes
Because beep codes can indicate only some of the problems in a
system at startup, most BIOSes also output a series of status codes
during the boot procedure. These codes are sent to an I/O port
address that can be read by specialized diagnostic cards, which you
can purchase from many different vendors. These POST cards (so
named from the power on self test) feature a two-digit LED panel
that displays the status codes output by the BIOS. The simpler
POST cards are hard-wired to pick up signals from the most commonly
used I/O port address 80hex, but more expensive models
can be adjusted with jumper blocks to use other addresses used by
certain BIOSes (such as Compaq).
These cards are normally sold with manuals that list the error/status
codes. While the cards are durable, the codes can become outdated.
To get an updated list of codes, contact the system or BIOS
vendor’s Web site.
Most POST cards have been based on the ISA bus, but the latest
models are now being made to fit into PCI slots because ISA is
becoming obsolete. For diagnosing portable systems, and to avoid
the need to open a system to insert a POST card, Ultra-X offers a
MicroPOST display unit that attaches to the parallel port. Contact
Ultra-X at www.uxd.com for more information.
Onscreen Error Messages
An onscreen error message is often the easiest of the error methods
to understand, because you don’t need to count beeps or open the
system to install a POST card. However, because some systems use
numeric error codes, and even “plain English” codes need interpretation,
these messages can still be a challenge to interpret. Because
the video circuits are tested after components such as the motherboard,
CPU, and BIOS, an onscreen error message is usually indicative
of a less-serious error than one that is reported with beep
codes.
Interpreting Error Codes and Messages
Because beep codes, error/status codes, and onscreen messages vary
a great deal by BIOS vendor (and sometimes BIOS model), you
must know what BIOS a system has before you can choose the correct
table. With major-brand systems (and some others), you’ll typically
find a list of error codes and messages in the system
documentation. You can also contact the BIOS or system vendors’
Web sites for this information, or check on the CD included with
Upgrading and Repairing PCs, 12th Edition.