IBM 5110 Troubleshooting Guide

This guide documents fault diagnosis for the IBM 5110 Computing System. The 5110 inherits the IBM 5100's PALM processor and integrated 5-inch CRT, so much of the troubleshooting practice translates directly from the 5100. The 5110 adds the external IBM 5114 Diskette Unit (8-inch floppy drives), IEEE-488 (HP-IB) bus, RS-232 channels, and EBCDIC encoding, each with their own diagnostic surface.

Reference Documents

• SY31-0553-2 — IBM 5110 System Maintenance Analysis Procedures (MAP), January 1979 — the per-symptom troubleshooting decision tree.
• SY31-0550-2 — IBM 5110 Computer Maintenance Information Manual (MIM), February 1979 — theory of operation and diagnostic procedures.
• SY31-0551-1 — IBM 5114 Diskette Unit Maintenance, January 1979 — 8-inch floppy drive diagnostics.
• SY31-0557-0 — IBM 5110 Async Communications, January 1978 — comms adapter diagnostics.
• SA21-9311-1 — Customer Support Functions, October 1978 — operator-level acceptance test.

Initial Diagnosis Workflow

5110 power-on sequence:

1. Power LED on rear illuminates.
2. PSU rails stabilise (5110 + 5114 if attached).
3. Executable ROS self-test runs.
4. Language interpreter loads from Language ROS.
5. Language banner ("BASIC READY" or "APL READY") appears on the 5-inch CRT.

If any of these does not occur, stop and diagnose at that stage.

Stage 1 — No Power

• Mains lead, switch, fuse check on the 5110.
• If a 5114 is attached, check the 5114 mains lead and switch separately — they have independent power.
• Verify PSU rails at the planar power connector.

Stage 2 — Power But No Display

Same diagnostic surface as the IBM 5100:

• Front-panel "Display Registers / RAM Hex" switch — confirms video chain.
• Reseat ROS / RWS / PALM cards.
• Check CRT anode HV.

Stage 3 — Banner Wrong / Garbled

• Language ROS bit error — reseat Language ROS.
• Toggle APL / BASIC — if one banner is clean and the other garbled, isolated to the failed Language ROS.
• On the 5110 the EBCDIC character set is in use — verify that the garble isn't actually correct EBCDIC characters being read as 5100 encoding.

Stage 4 — System Won't Read / Write Diskettes (5114)

• No drive activity at all — cable between 5110 and 5114 unseated, or 5114 PSU dead.
• Drive spins but won't read — head dirty; head alignment; drive belt slipping.
• Read OK, write produces unreadable diskettes — head alignment, write-protect sensor stuck.
• Sporadic CRC errors — drive belt aged, oxide shedding from old diskettes, head dirty.

Stage 5 — IEEE-488 Bus Not Working

• Cable unseated.
• Terminator missing or failed.
• IEEE-488 controller card on 5110 reseat.
• Test with a known-good instrument.

Diagnostic ROS

Same keyboard sequence at power-on as the IBM 5100; enters Diagnostic ROS for read / write access to RAM, video memory, PALM registers, interrupt vectors and clock counter.

The 5110 MIM SY31-0550 documents the Diagnostic ROS error codes specific to the 5110 (Section IV).

Customer Acceptance Test

The Customer Acceptance Test (CAT) for the 5110 is documented in SA21-9311-1 (Customer Support Functions). It uses a customer test diskette (on Model 2 or 3) or test tape cartridge (on Model 1) and exercises:

• RAM (full pattern test).
• Tape drive (Model 1).
• Diskette drives (5114, if attached).
• IEEE-488 bus (if cable + terminator present).
• RS-232 channels (loopback or external).
• Communications Adapter (if fitted).
• CRT and keyboard.

PALM Diagnosis

Same as the IBM 5100 — PALM gate arrays are unobtainium. Reseat the PALM edge connector before suspecting failure. PALM-specific check-stop codes in the MIM identify which gate array has failed when a failure is real.

ROS / RWS Memory Faults

• Garbled banner — Language ROS bit error.
• Refusal to complete Executable ROS self-test — Executable ROS bit error or PALM fault.
• RAM size mismatch on banner — RWS card failure; reseat each 16 KB module.

Tape Drive Faults (Model 1)

Same procedure as IBM 5100 Troubleshooting Guide. Belt, capstan, head, alignment, in that order.

8-Inch Floppy Drive Faults (5114)

• No drive activity — 5114 PSU dead, or cable to 5110 unseated.
• Drive spins but won't read — head dirty, alignment drift, drive belt slipping.
• Won't load head — head load solenoid fatigued or stuck.
• Write errors — write-protect sensor, head alignment.
• CRC errors — drive belt aged, oxide shedding from old Diskette 2D media, head dirty.
• Spindle won't spin — motor brushes worn.

The 5114 MIM SY31-0551 documents per-symptom diagnosis with FRU swap decision tree.

CRT Faults

Same as the IBM 5100 — flyback, deflection, cathode emission.

IEEE-488 Bus Diagnosis

• Bus hung — terminator missing or failed.
• Controller initialisation timeout — PALM IEEE-488 controller card; reseat or replace.
• Single instrument not responding — instrument address conflict; verify dipswitch settings on the instrument.
• All instruments timing out — cable, terminator, or 5110 IEEE-488 interface failure.

RS-232 / Async Communications Faults

The Async Communications Feature (SY31-0557) carries common RS-232 faults:

• Wrong baud rate — verify dipswitch settings on the adapter and target.
• Garbled output — parity, stop bits, character set mismatch.
• No output — cable; pin 2 / pin 3 swap.
• Cable wired straight-through vs crossed (null modem) — verify the target device's pinout.

Common Field Symptoms and Resolutions

• Won't power on — Mains, fuse, switch, PSU primary.
• Power LED but no display — PSU bulk filter caps shot; see IBM 5110 Capacitor Replacement Guide.
• Banner appears, system hangs on keystroke — keyboard or PALM input handling.
• Garbled banner — Language ROS or socket oxidation.
• Tape works on 5110 but data won't transfer to a 5100 — EBCDIC vs 5100-specific encoding mismatch (not a fault).
• 5114 floppy not detected — cable or 5114 PSU.
• Floppy reads OK but writes corrupt — head alignment; or aged diskette media.
• IEEE-488 instrument not responding — addressing, terminator, cable.
• Random reboots / hangs — bulk filter cap ESR rising; recap PSU.

Diagnostic Workflow Summary

1. Power on; observe LED, fan, display chain.
2. If no power on 5110, suspect 5110 PSU. If no power on 5114, suspect 5114 PSU.
3. If power but no display, suspect Executable ROS, PALM, or CRT chain.
4. If display but garbled banner, reseat ROS and try the other language.
5. Enter Diagnostic ROS and run the documented self-tests.
6. Run the Customer Acceptance Test from diskette (Model 2/3) or tape (Model 1).
7. Cross-reference any check-stop code against MAP document SY31-0553.

Architecture

The IBM 5110 is built around the IBM PALM (Program All Logic in Microcode) 16-bit processor, with its operating environment (APL and/or BASIC) held in microcode "read-only storage" (ROS). It is not PC-compatible and predates the IBM PC, so PC diagnostics do not apply — use the routines in the IBM Maintenance Information manual.

Power supply

This machine uses the internal PSU that converts 115 V AC to the system rails. Confirm every rail (the 5100/5110-type supply produces +12 V, −12 V, +8.5 V, +5.0 V and −5.0 V) before chasing logic faults. Ageing electrolytics are the usual failure — recap and re-check the rails.

Storage and display

The 5110 uses 8-inch floppy drives (internal or external) and has a small built-in CRT. Mechanisms need cleaning and belt/roller service; the IBM Maintenance Information manuals (on Bitsavers) give the full disassembly, adjustment and diagnostic procedures.

Related Pages

• IBM 5110
• IBM 5110 Maintenance Guide
• IBM 5110 Capacitor Replacement Guide
• IBM 5100 Troubleshooting Guide — most procedures translate directly

References

• Bitsavers — IBM 5110 documents.
• IBM 5110 — Wikipedia.
• IBM PALM processor — Wikipedia.
• Stuttgart Computermuseum — IBM 5110.