Editing IBM 3270 PC Maintenance Guide (section)

== Opening the System Unit ==

Identical to the [[IBM PC XT Maintenance Guide]]:

# Power off and unplug all cables (mains, keyboard, video, printer, BNC twinax to controller).
# Five Philips #2 screws on the rear panel.
# Slide cover '''forward''' to release.

The 3270 PC interior is densely populated. A typical full configuration occupies:

* Hard Disk Adapter (Models 006, 026, 070, 071 only — '''not''' 030 or 050, which are diskette-only).
* Diskette Drive Adapter.
* 3270 PC Display Adapter, or the '''3295 Plasma Display Adapter''' on Models 024 and 026.
* All-Points-Addressable card, where fitted.
* Programmed Symbols card, where fitted.
* 3278/79 Emulation Adapter — IBM calls it the '''DFCA''', the Distributed Function Communications Adapter.
* Keyboard Adapter, or the '''Plasma Keyboard Adapter''' on Models 024 and 026.
* Printer/Memory Adapter, or the '''XMA''' with 1 MB on Models 031, 051 and 071.

'''IBM does not publish a fixed slot order for the 5271''', so record the as-built configuration before you pull anything. One documented constraint: the XMA '''jumpered as LPT2 on a 5271 with a fixed disk is not supported''' — there is an interrupt-level conflict.<ref name="sim" />