Editing IBM 5110 Troubleshooting Guide

[[File:IBM 5110 (photo).jpg|thumb|right|300px|IBM 5110. Source: Wikimedia Commons.]]
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.<ref>http://bitsavers.org/pdf/ibm/5110/</ref>
* '''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:

# Power LED on rear illuminates.
# PSU rails stabilise (5110 + 5114 if attached).
# Executable ROS self-test runs.
# Language interpreter loads from Language ROS.
# 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.<ref>https://en.wikipedia.org/wiki/IBM_5100</ref>

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 ==

# Power on; observe LED, fan, display chain.
# If no power on 5110, suspect 5110 PSU. If no power on 5114, suspect 5114 PSU.
# If power but no display, suspect Executable ROS, PALM, or CRT chain.
# If display but garbled banner, reseat ROS and try the other language.
# Enter Diagnostic ROS and run the documented self-tests.
# Run the Customer Acceptance Test from diskette (Model 2/3) or tape (Model 1).
# 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.<ref name="ibm51">[https://voidstar.blog/ibm-5100-power-supply/ IBM 5100 Power Supply], voidstar; [https://en.wikipedia.org/wiki/IBM_PALM_processor IBM PALM processor], Wikipedia; and the IBM 5110/5120 Maintenance Information manuals on [https://bitsavers.org/pdf/ibm/ Bitsavers]. Source for the PALM architecture, the five-rail PSU, and the 5120 dual power supplies.</ref>

== 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.<ref name="ibm51">[https://voidstar.blog/ibm-5100-power-supply/ IBM 5100 Power Supply], voidstar; [https://en.wikipedia.org/wiki/IBM_PALM_processor IBM PALM processor], Wikipedia; and the IBM 5110/5120 Maintenance Information manuals on [https://bitsavers.org/pdf/ibm/ Bitsavers]. Source for the PALM architecture, the five-rail PSU, and the 5120 dual power supplies.</ref>

== 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.<ref name="ibm51">[https://voidstar.blog/ibm-5100-power-supply/ IBM 5100 Power Supply], voidstar; [https://en.wikipedia.org/wiki/IBM_PALM_processor IBM PALM processor], Wikipedia; and the IBM 5110/5120 Maintenance Information manuals on [https://bitsavers.org/pdf/ibm/ Bitsavers]. Source for the PALM architecture, the five-rail PSU, and the 5120 dual power supplies.</ref>

== References ==

<references />

== Related Pages ==

* [[IBM 5110]]
* [[IBM 5110 Maintenance Guide]]
* [[IBM 5110 Capacitor Replacement Guide]]
* [[IBM 5100 Troubleshooting Guide]] — most procedures translate directly

== References ==

* [http://bitsavers.org/pdf/ibm/5110/ Bitsavers — IBM 5110 documents].
* [https://en.wikipedia.org/wiki/IBM_5110 IBM 5110 — Wikipedia].
* [https://en.wikipedia.org/wiki/IBM_PALM_processor IBM PALM processor — Wikipedia].
* [https://computermuseum.informatik.uni-stuttgart.de/dev_en/ibm_5110/ibm_5110.html Stuttgart Computermuseum — IBM 5110].

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