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IBM System 23 Diagnostic User Guide

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The IBM System/23 Diagnostic User Guide, part number 6841631 (April 1982 edition, EC 327594), is the customer-engineer diagnostic manual for the IBM System/23 Datamaster with diskette. It is the authoritative source for the PID 1200 Processor Power-On Test — the routine every Datamaster runs at power-on — and for the diskette-resident diagnostic programs.

What it contains

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  • PID 1200, Processor Power-On Test — the purpose, the run time, the complete index of routines with the area each one tests and whether it is critical, the two program-option jumpers, and the error-reporting mechanism.
  • PID 1500 — the ROS-resident diskette drive test.
  • Diagnostic Control Program (DCP), the FLT diagnostic programs and the CE utility programs, with their menus and options.
  • Error logs, read/write statistics and the ROS EC and part-number display.

The parts most often needed

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PID 1200 runs for 25 to 35 seconds, depending on configuration, and it runs at every power-on or whenever program flow branches to location 0000.

Errors are reported two different ways, depending on how far the test got. Before the CRT is started — routines 01 to 06 — an error stops the machine and leaves a code in a set of hardware latches, which the engineer probes. Once the CRT is running, the same codes are displayed on the screen, and the display attribute tells you what kind of failure it is:

  • Normal — the routine ran without error.
  • Flashing reverse video — an error in a part critical to operation. The system stops after finishing the power-on sequence.
  • Reverse video — an error in a part that is not critical. Pressing ERROR RESET lets initialisation continue.
  • Underline — the feature that routine tests is not fitted. This is not a fault.

And the rule that saves the most time: if a TRAP occurs during power-on testing, the failure is in the routine after the last one displayed — not the one you are looking at.

Two CE jumpers on the CPU board change the behaviour: loop (repeat until the jumper is removed — disconnect the external diskette attachment cable first) and stop on error (halt after the failure indicator appears). IBM recommends fitting the stop-on-error jumper whenever the loop jumper is fitted and the machine is left unattended.

Download the guide here: IBM System 23 Diagnostic User Guide 6841631.pdf

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