Editing IBM 3270 PC Maintenance Guide (section)

== What IBM's Error Codes Mean ==

The 5271 posts codes that a plain XT does not, and IBM maps each range to a field-replaceable unit:<ref name="sim" />

* '''28XX''' — the DFCA (3278/79 Emulation Adapter).
* '''32XX''' — Display Adapter, Programmed Symbols Adapter, All-Points-Addressable Adapter, or the Top Card Connector.
* '''44XX''' — Display Attachment Unit (on the [[IBM 3270 PC/G|/G]] and [[IBM 3270 PC/GX|/GX]], not the base 5271).
* '''45XX''' — IEEE Interface Adapter card.

Two of these lie to you:

* '''A false 2801.''' If a long DFCA has been replaced with the newer short card, the '''Keyboard Timer Adapter''' may need changing too. Press F1 to continue after POST; if the host session then establishes normally, the 2801 is false. ECA001 directs the engineer to order '''P/N 1497249''' (one EPROM) and replace the pluggable EPROM on the Keyboard Timer Adapter.<ref name="sim" />
* '''A false 8505.''' The XMA diagnostic tests D000&ndash;DFFF; any other adapter with RAM or ROS in that range produces an 8505 that is not a real fault.<ref name="sim" />

A plain 83-key XT keyboard in place of the 5271 Keyboard Element produces POST error '''302''' — press F1 to continue.<ref name="seasip" />