Editing IBM PC XT Troubleshooting Guide (section)

== Numeric POST Error Codes ==

The XT uses the same IBM POST numeric error code convention as the 5150 and the AT. The code format is "XYZZ" where the first one or two digits identify the failing subsystem (the "device number") and the remainder describes the specific failure. The device number followed by 00 indicates a successful test pass for that device.

=== 1xx — System board errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 101 || System board failed
|-
| 102 || BIOS ROM checksum error
|-
| 103 || BASIC ROM checksum error
|-
| 104 || Interrupt controller
|-
| 105 || Timer
|-
| 106 || Converting logic test failure
|-
| 107 || Adapter card or math coprocessor (NMI)
|-
| 108 || Timer bus test
|-
| 109 || DMA test error
|-
| 121 || Unexpected hardware interrupt
|-
| 131 || Cassette wrap test failed (rarely seen on XT — XT has no cassette port)
|-
| 199 || User indicated configuration not correct
|}

=== 2xx — RAM errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 201 || Memory test error. The format ''xyzz'' indicates failing bank and bit position.
|-
| 202 || Memory address error (address lines 0-15)
|-
| 203 || Memory address error (address lines 16-23)
|}

=== 3xx — Keyboard errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 301 || Keyboard did not respond to software reset, or a stuck key. A number preceding 301 is the scan code of the stuck key.
|-
| 302 || User indicated keyboard error
|-
| 303 || Keyboard or system board error
|}

=== 4xx — Monochrome display adapter errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 401 || [[IBM Monochrome Display Adapter|MDA]] memory test, horizontal sync, or video test failed
|-
| 408 || User indicated display attributes failure
|-
| 416 || User indicated character set failure
|-
| 424 || User indicated 80×25 mode failure
|-
| 432 || Parallel port test failed (printer port on the MDA)
|}

=== 5xx — Colour graphics adapter errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 501 || [[IBM Color Graphics Adapter|CGA]] memory test, horizontal sync, or video test failed
|-
| 508-564 || User-indicated CGA display attribute, character set, mode, and light-pen test failures
|}

=== 6xx — Diskette drive / adapter errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 601 || [[IBM FDD Adapter|FDD adapter]] power-on diagnostics test failed
|-
| 602 || Diskette test failed (boot record not valid)
|-
| 606 || Diskette verify function failed
|-
| 607 || Write-protected diskette
|-
| 611 || Time-out (diskette status returned)
|-
| 613 || Bad DMA (diskette status returned)
|-
| 621 || Bad seek (diskette status returned)
|-
| 622 || Bad CRC (diskette status returned)
|-
| 623 || Record not found
|-
| 624 || Bad address mark
|}

=== 7xx — 8087 math coprocessor errors ===

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 701 || 8087 coprocessor test failure. If no 8087 is fitted, set SW1 bit 2 to OFF.
|}

=== 9xx / 11xx / 13xx / 14xx — Other adapters ===

* '''901''' — Parallel printer adapter test failed.
* '''1101-1157''' — Asynchronous (RS-232) communications adapter test failures (the XT shipped with this card as standard).
* '''1301''' — Game adapter test failed.
* '''1401, 1404''' — Printer / matrix printer test failures.

=== 17xx — Fixed disk (hard drive) errors ===

Of particular relevance for the XT, which shipped with an MFM hard drive on most submodels.

{| class="wikitable styled-table" style="width:100%; text-align:left;"
! Code !! Meaning
|-
| 1701 || [[IBM Fixed Disk Adapter|Fixed Disk Adapter]] POST error — controller cannot communicate with the drive
|-
| 1702 || Adapter error
|-
| 1703 || Drive error (seek)
|-
| 1704 || Adapter or drive error
|-
| 1705 || No record found
|-
| 1706 || Write fault error
|-
| 1707 || Track 0 error
|-
| 1708 || Head select error
|-
| 1710 || Read buffer overrun
|-
| 1711 || Bad address mark
|-
| 1713 || Data compare error
|-
| 1714 || Drive not ready
|-
| 1780, 1781 || Disk 0 / Disk 1 failure
|-
| 1782 || Disk controller failure
|}

=== 18xx — I/O Expansion Unit errors (5161) ===

* '''1801''' — IBM 5161 Expansion Unit POST error. '''Also''' generated by a non-slot-8-compatible card placed in slot 8 of the 5160 motherboard.
* '''1810-1821''' — various I/O extender / receiver card faults.