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IBM 5322 Computer Service Manual

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The IBM 5322 Computer Service Manual, order number SY34-0171-0 (December 1980), is IBM's field service manual for the IBM 5322 computer — the processing unit of the IBM System/23 Datamaster system. It is Volume 1 of the IBM System/23 Service Library.

What it contains

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  • Chapter 2, processor, processor features and power supply — locations (1200), AC voltage distribution diagrams for all three supply variants (1210), the DC voltage distribution diagram with IBM's voltage tolerance and ripple table (1211), signal cable distribution (1212), covers (1220), CPU planar board and its connector pin assignments (1230), and the power supply removal, fuse and power switch procedures for each of the three supplies (1240 to 1265). Then a theory of operation covering the model numbers, standard and optional features, external I/O devices and the CPU.
  • Chapter 3, keyboard — the 83-key capacitive keyboard and its matrix.
  • Chapter 4, CRT display unit — the 305 mm (12 in.) display.
  • Chapter 5, diskette drives — including the AC drive motor, its run capacitor (1551), the drive belt and pulley, and the stepper drive motor.

Why it matters

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It shows that the Datamaster's power supply is ferroresonant, not linear. The layout diagram names a resonant capacitor C6, the AC distribution diagrams show a tapped transformer with jumper-selected mains taps, and IBM prints a DANGER notice reading "Up to 800 Vac is generated in the power supply". Descriptions of the 5322 as a transformer-bridge-and-series-pass-regulator design — including the ones that used to be on this wiki — are wrong, and matter, because a ferroresonant supply behaves differently under fault and carries a hazard a linear supply does not.

It also gives figures that can be checked with a meter:

  • Per-rail DC fuses — F1 −5 V (0.5 A), F2 +12 V (1.5 A), F3 −12 V (0.5 A), F4 +24 V (1.5 A), F5 +5 V (10 A), and F6 on the AC input.
  • Voltage tolerances and peak-to-peak ripple limits for every rail.
  • A ripple measurement method using an ordinary service meter with a 0.22 µF capacitor in series with one lead, for anyone without a scope.
  • Three supply part numbers, 6838279, 6838280 and 6838281, with different fuse layouts and mains-tap tables.

What it does not contain

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No capacitance values, anywhere. The supply's A1 card is treated as an assembly; the only capacitors identified by designator are the resonant capacitor C6 in the supply and the AC drive motor run capacitor in each diskette drive, and neither is given a value. There is no component-level parts list in this volume.

Download the manual here: IBM 5322 Computer Service Manual SY34-0171-0.pdf

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