IBM PC AT 5170 Technical Reference (March 1984)

The IBM Personal Computer AT Technical Reference, First Edition (March 1984), IBM part number 1502243, is the 462-page technical reference for the IBM PC AT 5170 as originally shipped: the Type 1 system board with the 01/10/84 BIOS.

What it contains

• Section 1, System Board (1-1) — memory and the 80286, system performance (1-7), system timers, system interrupts with the hardware interrupt listing and interrupt sharing (1-14), the ROM and RAM subsystems, DMA, the I/O channel (1-15 to 1-30), other circuits including the speaker, the jumper, the type of display adapter switch (1-31), the variable capacitor (1-31) and the keyboard controller, then specifications (1-55), connectors (1-57) and the logic diagrams (1-61).
• Section 2, Coprocessor — the 80287.
• Section 3, Power Supply (3-1) — inputs, outputs, output protection, the dummy load, output voltage sequencing, no-load operation, the power-good signal, fan-out and the connectors.
• Section 4, Keyboard — the interface, key-code scanning, the buffer, the power-on reset and basic assurance test, commands in both directions, key scan codes, clock and data signals, the keyboard layout and the connector specification.
• Section 5, System BIOS — usage, keyboard encoding and the BIOS listing.
• Section 6 — the 80286 instruction set.

What it does not contain

Not a service manual: no FRU part numbers, no removal procedures, no symptom-to-FRU index. The logic diagrams are design drawings without a populated bill of materials.

It documents only the Type 1 board and the 01/10/84 BIOS. If your AT has a Type 2 (Baby AT) planar or a later BIOS, use the September 1985 edition instead — the differences are real and this edition will mislead you.

What it settles

Two AT-specific details that are frequently mis-stated elsewhere and are settled here:

• The "variable capacitor" (1-31) is a real, documented part of the AT planar, not a modification. It appears in Section 1 alongside the jumper and the display-type switch.
• The dummy load and no-load operation clauses in Section 3 explain why an AT supply may behave oddly on the bench with nothing connected: IBM specifies its behaviour under no load explicitly, so a supply that misbehaves unloaded is not necessarily faulty.

Download it here: IBM PC AT 5170 Technical Reference Mar84.pdf

Related pages

• IBM PC AT (5170) · IBM PC AT Maintenance Guide · IBM PC AT Troubleshooting Guide · IBM PC AT Capacitor Replacement Guide
• IBM PC AT 5170 Technical Reference (September 1985) — the later edition, covering all board types
• IBM PC 5150 Technical Reference · IBM PC XT Technical Reference (First Edition)