Editing IBM 3270 PC Maintenance Guide (section)

== Card Inventory at Service Time ==

For each service visit, verify the card complement and check the as-built ROMs:

# '''Keyboard Adapter''' — two ROM variants: '''6323581''' (simple) or '''6323582''' (complicated, with NMI button and serial port). '''This card holds the video BIOS''' for the 3270 PC Display Adapter; without it the video cards do nothing, which is the single most confusing failure mode on this machine.<ref name="seasip">John Elliott, [http://www.seasip.info/VintagePC/5271.html The IBM 5271 (aka 3270 PC)], seasip.info. A community technical reference built from a working machine: the card complement and what each card does, the video BIOS living in the keyboard controller ROM (part 6323581 for the "simple" controller and 6323582 for the "complicated" one), the error codes 3201, 3202, 3203 and 2801, the 5272 display timings, and the statement that the case, motherboard, drives and power supply are all identical or very similar to the XT.</ref> Models 024 and 026 use a '''Plasma Keyboard Adapter''' instead.<ref name="sim" />
# '''3270 PC Display Adapter''' — SCN2672 PVTC at 0180h–019Bh. Inspect the SCN2672 socket for oxidation.
# '''APA card''' (where fitted) — adds CGA modes + 3270-PC graphics modes.
# '''PSS card''' (where fitted) — Programmed Symbol Set, RAM-loaded fonts.
# '''3278/79 Emulation Adapter''' — I/O at 2D0h–2D6h (older) or 2D0h–2D7h (newer). BNC twinax to controller.