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Deep technical pre-PC IBM page with verified sources (Bitsavers MIM/MAP, Wikipedia, IBM Archives) — honest gap disclosure where IBM did not publish per-board cap values

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This guide documents preventive maintenance for the '''[[IBM 5110]] Computing System''' (announced January 1978). The 5110 shares its PALM processor, integrated 5-inch CRT, and core architecture with the [[IBM 5100]] — much of the maintenance practice translates directly. The 5110 adds external diskette support via the IBM 5114 Diskette Unit, IEEE-488 (HP-IB), RS-232 channels, and EBCDIC character encoding, all of which add their own maintenance surface.

== Safety Warning ==

The 5110 PSU is a '''linear''' supply with large bulk filter capacitors that hold a charge after power-off. The 5114 Diskette Unit has its own separate linear PSU. Before any work inside either chassis:

# Power off and unplug the mains lead.
# Wait at least 30 seconds.
# Discharge each bulk filter capacitor through a 1 kΩ / 5 W resistor.
# Verify with a multimeter.

The internal 5-inch CRT carries high voltage on the flyback transformer and anode. Discharge the CRT anode to chassis ground via a high-voltage probe before any work on the deflection / flyback board.

== Documentation Set ==

* '''SY31-0550-2''' — IBM 5110 Computer Maintenance Information Manual (MIM), February 1979 — the CE service manual.<ref>http://bitsavers.org/pdf/ibm/5110/</ref>
* '''SY31-0553-2''' — IBM 5110 System Maintenance Analysis Procedures (MAP), January 1979.
* '''SY31-0551-1''' — IBM 5114 Diskette Unit Maintenance, January 1979.
* '''SY31-0557-0''' — IBM 5110 Async Communications, January 1978.
* '''SA21-9311-1''' — Customer Support Functions, October 1978 (operator-level procedures).
* '''GH30-0232-1''' — IBM 5110 / 5120 Bibliography, September 1980 — master reference list.

Download all of these for any serious 5110 restoration.

== Opening the System Unit ==

Tools: Philips #2 screwdriver, T15 / T20 Torx, anti-static strap, high-voltage probe.

The 5110 chassis is the same as the [[IBM 5100]]:

# Power off and unplug all cables.
# Remove the cover fasteners on the rear and bottom.
# Lift the upper shell carefully — the 5-inch CRT and deflection board are mounted in the upper shell.
# Inside layout matches the 5100: PSU at left rear, PALM board centre, ROS / RWS cards behind, DC300 drive (Model 1) at front.

== Opening the 5114 Diskette Unit ==

The 5114 is a separate enclosure with:

* Linear PSU for diskette spindle and head-load electronics.
* 1 or 2 × 8-inch floppy drives (typically Shugart-class drives in IBM cosmetics).
* Drive controller card.
* Cable to the 5110 main unit.

# Power off and unplug the 5114 mains lead.
# Wait 30 seconds and discharge the 5114 PSU bulk caps.
# Remove the cover screws on the 5114 enclosure.
# Lift cover to expose the drives, PSU and controller card.

== Inspecting the Chassis ==

Items in order:

# '''Main PSU bulk filter capacitors''' — visual inspection for bulging, leaks, discolouration.
# '''Series-pass regulator transistors''' — heatsink-mounted; check thermal paste.
# '''Flyback / deflection board''' — inspect for cracked solder joints.
# '''DC300 tape drive belt''' (Model 1) — replace if perished.
# '''Keyboard''' — IBM beam-spring; foam pads may have degraded.
# '''CRT''' — inspect for emission loss.
# '''ROS modules''' — reseat in their sockets (oxidised pins).
# '''PALM board edge connector''' — reseat (most common cause of "dead PALM" symptoms).

For the 5114:

# '''Diskette spindle motor brushes''' — inspect through brush holders.
# '''Drive belt''' on the 8-inch floppy drives — replace if perished.
# '''Head load solenoid''' — verify operation.
# '''Drive logic board electrolytics''' — inspect.

== Regular Cleaning ==

Same procedures as the [[IBM 5100]]:

* Soft brush and compressed air for the planar, PALM board, ROS / RWS cards, and PSU vents.
* No compressed air over leaking electrolytics.
* Wipe keyboard with microfibre; remove keycaps with the IBM tool.
* Clean DC300 tape head with IPA on a foam swab.
* Clean 8-inch floppy heads with IPA on a foam swab.

== PSU Voltage Checks ==

Probe each rail at the planar power connector. Tolerances (typical linear PSU):

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''IBM 5110 PSU rail tolerances'''
! Rail !! Approximate target
|-
| +5 V (logic) || +4.75 V to +5.25 V
|-
| +12 V || +11.4 V to +12.6 V
|-
| −5 V / −12 V || As marked in MIM SY31-0550
|-
| CRT high-voltage anode || ~9–11 kV (5-inch CRT)
|}

Out-of-tolerance rails after recapping bulk caps suggest a series-pass regulator transistor failure.

The 5114 has its own PSU with rails appropriate for the 8-inch floppy drives:

* '''+5 V''' for drive logic.
* '''+12 V''' or '''+24 V''' for spindle motor and head load solenoid (depends on drive vendor).
* '''−5 V''' bias rail.

Verify per the 5114 MIM SY31-0551.

== DC300 Tape Drive Maintenance (Model 1) ==

Same procedure as the [[IBM 5100 Maintenance Guide]]:

* Drive belt replacement (urethane perishes).
* Capstan rubber clean or replace.
* Head clean and alignment.
* Erase head clean.

== 5114 Diskette Drive Maintenance ==

* '''Drive belt''' on 8-inch floppy — replace if perished. Modern replacements available from the 8-inch floppy restoration community.
* '''Head load solenoid''' — exercise it; replace if fatigued.
* '''Spindle motor''' — brush wear is the main failure mode; brushes can be re-sourced from industrial motor suppliers.
* '''Read / write head''' — clean with IPA on foam swab. Never use cotton — fibres in the head gap cause errors.
* '''Head alignment''' — verify against a known-good diskette using the procedure in the 5114 MIM.
* '''Oxide shedding''' from old diskettes — period IBM Diskette 2D media may have lost binder integrity. Inspect every diskette before reading; if oxide is shedding, do not load it (will contaminate the head).

== EBCDIC Note ==

The 5110 uses '''EBCDIC encoding''' throughout, which makes its software at the byte level partially incompatible with the 5100's. If you are loading data from a 5100, format-shift it first; the 5110 cannot directly read 5100 5100-specific-code data.

== IEEE-488 Bus Maintenance ==

The 5110 carries an IEEE-488 (GP-IB / HP-IB) bus connector. Maintenance items:

* Clean the connector with deoxidising contact cleaner.
* Verify the bus terminator if present.
* Test with a known-good IEEE-488 instrument before suspecting the 5110 bus interface.

== ROS and RWS Module Care ==

Same as the [[IBM 5100]]:

* Static-sensitive — always wear an anti-static strap.
* Do not flex ROS modules.
* Reseat ROS cards if intermittent — oxidised socket pins cause garbled language banners.

== PALM Board Care ==

Same as the [[IBM 5100]]: 13 bipolar gate arrays are unobtainium. Reseat the PALM board edge connector if intermittent before suspecting gate array failure.

== CRT Maintenance ==

Same as the [[IBM 5100]] — 5-inch internal CRT and deflection / flyback board mounted in the upper shell.

== Recommended Tools ==

* Philips #2 and T15 / T20 Torx screwdrivers.
* Anti-static strap.
* Digital multimeter with HV-rated probe.
* High-voltage probe for CRT discharge.
* IPA + foam swabs.
* Soldering iron (fine tip) + solder wick.
* DC300 cartridge head-cleaning kit (Model 1).
* 8-inch floppy head-cleaning supplies (5114).
* Modern QIC-class replacement belt for the DC300 drive.
* Modern 8-inch floppy drive belt replacement.
* MIM SY31-0550 and SY31-0551 PDFs.

== Related Pages ==

* [[IBM 5110]]
* [[IBM 5110 Troubleshooting Guide]]
* [[IBM 5110 Capacitor Replacement Guide]]
* [[IBM 5100 Maintenance Guide]] — common chassis procedures
* [[Recommended Tools]]

== References ==

* [http://bitsavers.org/pdf/ibm/5110/ Bitsavers — IBM 5110 documents]. MIM SY31-0550, MAP SY31-0553, 5114 MIM SY31-0551.
* [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]. Restoration notes.

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[[Category:IBM]]
[[Category:Maintenance Guides]]

IBM 5110 Maintenance Guide - Revision history

Josh: Deep technical pre-PC IBM page with verified sources (Bitsavers MIM/MAP, Wikipedia, IBM Archives) — honest gap disclosure where IBM did not publish per-board cap values