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AST RESEARCH TECHNICAL BULLETIN TB-0055 9-21-84
FAULT ISOLATION OF THE IBM PC-1
USING THE POWER ON SELF TEST (POST) DIAGNOSTICS
Each time the IBM PC-1 (64K motherboard) is powered on, the ROM
BIOS initiates a built-in set of diagnostic tests to determine
the functionality of the hardware.
These tests are also performed (with the exception of the RAM
test) each time a "warm boot" is initiated (Ctrl-Alt-Del).
Failures to the diagnostic tests can be caused by component
failures on the system motherboard, errors in switch settings, or
a defective expansion board. These failures are indicated by a
sequence of beeps, error codes on the CRT display or both.
The attached tables present the tests in the order in which they
are performed. Thus, if an error is detected, fault isolation
can be accomplished as the tests above the failure have been
completed successfully.
Table 1 is applicable to an IBM PC-1, which is NOT fitted with
either a "bootable" harddisk or an IBM Expansion Chassis.
Table 2 is applicable to an IBM PC-1, which is fitted with either
a "bootable" harddisk or an IBM Expansion Chassis.
TABLE 1
POST ERRORS FOR IBM PC-1 WITHOUT EITHER AN
IBM EXPANSION CHASSIS OR A BOOTABLE HARDDISK
SYMPTOM CAUSE
1. System does not respond The power supply has shut
at all when turned on. down,
OR:
The 8088 has HALTed due to:
- Internal 8088 problem.
- BIOS ROM checksum error.
- 8253 timer problem.
- 8237 DMA controller error.
- Error in last 16K of RAM.
Note: Try turning off power
supply, waiting 5 seconds,
then turning it on.
2. System beeps: The 8088 has HALTed due to:
1 long beep (3 seconds), - 8259 interrupt controller
1 short beep (1 second), error.
then stops. - 8253 timer counting too
fast or slow.
3. System beeps: Checksum error in a BASIC ROM.
1 long beep (3 seconds),
1 short beep (1 second),
but continues the power-
up sequence.
4. System beeps: Error in video RAM or error in
1 long beep (3 seconds), 6845 video circuitry.
2 short beeps (1 second
each), continues power-
up sequence.
5. System beeps: The display card is probably not
1 long beep (3 seconds), installed.
2 short beeps (1 second),
1 long beep (3 seconds),
2 short beeps (1 second
each).
6. 'XXYY 201' appears at the RAM error. XX = the high order
top of the display, where byte of the failing segment,
XXYY = four hexadecimal e.g.; XX = 20 would indicate
digits. that the error occurred between
segment 2000 and segment 2400.
(Memory is tested in 16K
blocks, each 64K increments the
segment by 1000. YY = the
failing bit pattern, which can
isolate the specific RAM.)
7. 'XX 301' appears at the Keyboard error. Usually a stuck
top of the display, where key, where XX = scan code of
XX = two hexadecimal digits. the stuck key.
8. '131' appears on display. Cassette port error.
9. '601' appears on display. Disk drive A, or disk adapter
error.
10. 'PARITY CHECK 1' appears. A RAM parity error has occurred
on the system motherboard. The
INT 2 routine in the BIOS gains
control and HALTs the 8088 when
a memory parity error occurs.
Parity checking had been
DISABLED prior to this point in
the test sequence, and is en-
abled here just before reading
the boot record from the disk.
11. 'PARITY CHECK 2' appears A RAM parity error has occurred
on the display. on an add-on memory board. This
message comes from the BIOS
ROM's INT 2 routine, which then
HALTs the 8088.
12. System beeps: This is normal system reponse
1 short beep (1 second). just before the system boots
from the disk. The system has
successfully passed the diag-
nostics.
TABLE 2
POST ERRORS FOR IBM PC-1 WITH AN IBM
EXPANSION CHASSIS OR A BOOTABLE HARDDISK
SYMPTOM CAUSE
1. System does not respond The power supply has shut down,
at all when turned on. OR:
The 8088 has HALTed due to:
- Internal 8088 problem.
- BIOS ROM checksum error.
- 8253 timer problem.
- 8237 DMA controller error.
- Error in last 16K of RAM.
Note: Try turning off power
supply, waiting 5 sec-
onds then turning it on.
2. System beeps: The 8088 has HALTed due to:
1 long beep (3 seconds), - 8259 interrupt controller
1 short beep (1 second), error.
then stops. - 8253 timer counting too
fast or slow.
3. System beeps: Error in video RAM or error in
1 long beep (3 seconds), 6845 video circuitry.
2 short beeps (1 second
each), continues power-
up sequence.
4. '1801' appears at the top Error in expansion unit inter-
of display. (If IBM Expan- face.
sion Unit is installed).
5. 'XXYY 201' appears at the RAM error. XX = the high
top of the display, where order byte of the failing seg-
XXYY = four hexadecimal ment, e.g.; XX = 20 would in-
digits. dicate that the error occurred
between segment 2000 and seg-
ment 2400. (Memory is tested
in 16K blocks; each 64K incre-
ments the segment by 1000.
YY = the failing bit pattern,
which can isolate the specific
RAM).
6. 'XX 301' appears at the Keyboard error; usually a
top of the display, where stuck key, where XX = the scan
XXYY = four hexidecimal code of the stuck key.
digits.
7. '131' appears on the display. Cassette port error.
8. '1701' appears on the IBM Fixed Disk error.
display.
9. System beeps; Checksum error in BASIC ROM.
1 long beep (3 seconds),
2 short beeps (1 second
each), and 'ROM' appears
on the display.
10. '601' appears on display. Disk drive A, or disk adapter.
11. 'PARITY CHECK 1' appears. A RAM parity error has occur-
red on the system motherboard.
The INT 2 routine in the BIOS
gains control and HALTs the
8088 when a memory parity
error occurs. Parity checking
had been DISABLED prior to this
point in the test sequence, and
is enabled here just before
reading the boot record from
the disk.
12. 'PARITY CHECK 2' appears A RAM parity error has occurred
on the display. on an add-on memory board. This
message comes from the BIOS
ROM's INT routine, which then
HALTS the 8088.
13. System beeps: This is normal system response
1 short beep (1 second). just before the system boots
from the disk. The system has
successfully passed the diag-
nostics.