IBM 3270 PC AT/G and AT/GX Maintenance Information

IBM 3270 Personal Computer AT/G and AT/GX Maintenance Information, order number SY33-0125-1 (June 1986), is IBM's field service manual for the 5373 system unit, the IBM 5378 Display Attachment Unit and the IBM 5379 19-inch display. 558 pages.

It is also the best surviving source for the XT-based IBM 3270 PC/GX, because the /GX uses exactly the same 5378 Display Attachment Unit and 5379 display; only the system unit differs (5371 instead of 5373). The dedicated /GX manual, SY33-0111, has not been located online.

What it contains

CRT handling and EHT safety procedures, including IBM's warning that some CRTs build a second capacitive charge after the first discharge and must be discharged again immediately before removal.
Maintenance analysis procedures for the 5378 — the four power-supply LEDs, the +12 V limits at the fan connector, the interconnect card P3 pinout (+5 V, +5 V sense, +12 V, −12 V, −5.2 V and return), and the short-hunting sequence for a supply that will not come up.
Locations — the 5378 A and B gate pin locator, the 5378 card plugging chart, and the system board diagrams.
Removals and replacements for the 5379 cards, CRT, yoke and EHT cable.
Chapter 7, the parts catalogue — the 5379 display broken down to individual cards (power supply card, primary power supply assembly, video amplifier card, deflection amplifier card, CRT socket card, manual controls card, degauss coil, EHT cable, fan) and the 5378 broken down to its power supply assembly, its 6 A slow-blow 250 V fuse, its two 12 V fans, its logic boards and its interconnect card.

What it does not contain

No capacitance values and no schematics. Even at its most detailed the manual stops at the card, and the 5378's power supply is a single assembly.

Download the IBM 3270 PC AT/G and AT/GX Maintenance Information here: IBM 3270 PC AT G and GX Maintenance Information SY33-0125-1.pdf

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