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.