IBM 5110 Capacitor Replacement Guide

This guide documents capacitor diagnosis and replacement for the IBM 5110 Computing System and its companion IBM 5114 Diskette Unit. The 5110 uses the same linear PSU topology as the IBM 5100 — large bulk filter capacitors after the bridge rectifier, linear series-pass regulators. The 5114 has its own separate linear PSU for the 8-inch floppy drives. After 45+ years, all electrolytics in both PSUs should be considered out of specification.

Important Caveat

Per-board exact capacitor values for the IBM 5110 and IBM 5114 are NOT published in surviving IBM documentation that this guide author has been able to locate. The Maintenance Information Manuals SY31-0550-2 (5110) and SY31-0551-1 (5114) document the PSUs as block diagrams without per-component values; the Parts Catalog S131-0626-1 lists capacitors by IBM part number, not by capacitance / voltage / type. This guide therefore documents the typical linear-PSU practice that applies to recapping the 5110 family, with categories of capacitor and representative value ranges. Each restorer should pull each board, identify caps in situ by their printed markings, and replace with same-or-higher voltage and same capacitance.

Safety Warning

The 5110 PSU and the 5114 PSU both contain mains-rectified bulk capacitors that hold a lethal charge after power-off. Before any PSU work on either unit:

1. Power off and unplug the mains lead.
2. Wait at least 30 seconds.
3. Discharge each bulk filter capacitor through a 1 kΩ / 5 W resistor.
4. 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.

Linear PSU Topology

Both the 5110 and 5114 PSUs are single-board linear supplies with:

• Mains input — input fuse, X2 line-suppression capacitor, mains transformer.
• Rectifier — bridge diodes on the secondary.
• Bulk filter — large axial-can aluminium electrolytics.
• Series-pass regulators — bipolar pass transistors on heatsinks.
• Output filtering — smaller electrolytics at rail output.

5110 Main PSU Bulk Filter Capacitors — Primary Target

The bulk filter capacitors after the bridge rectifier are the primary recap target on the 5110. Representative values (not IBM-published):

IBM 5110 main PSU bulk filter capacitor (representative)

Value	Voltage	Type	Position	Quantity (approx)
2200–4700 µF	25–50 V	Axial-can aluminium electrolytic, 105 °C	+5 V rail bulk after bridge	1
2200–4700 µF	25–50 V	Axial-can aluminium electrolytic, 105 °C	+12 V / −12 V rail bulk × 2	2
1000–2200 µF	16–35 V	Axial-can aluminium electrolytic, 105 °C	Auxiliary rail bulk	1–2

5110 Series-Pass Regulator Capacitors

IBM 5110 series-pass regulator capacitors (representative)

Value	Voltage	Type	Position	Quantity (approx)
47–470 µF	25–35 V	Aluminium electrolytic, 105 °C	Regulator input / output	4–6
0.1–1 µF	50 V	Film / tantalum bypass (inspect only)	Regulator bypass	4–6

5114 Diskette Unit PSU Capacitors

The 5114 PSU is larger than the 5110's because it drives 1 or 2 × 8-inch floppy drives (spindle motors + head load solenoids draw significant current). Representative values:

IBM 5114 PSU capacitor (representative)

Value	Voltage	Type	Position
4700–10000 µF	25–50 V	Axial-can aluminium electrolytic, 105 °C	+12 V or +24 V spindle rail bulk
2200–4700 µF	16 V	Aluminium electrolytic, 105 °C	+5 V drive logic rail bulk
100–470 µF	35 V	Aluminium electrolytic, 105 °C	Head load solenoid driver
47–220 µF	16 V	Aluminium electrolytic, 105 °C	Auxiliary
220 µF	200 V	Aluminium electrolytic, 105 °C	Primary bulk (lethal-charge component)
0.1 µF	275 VAC	X2 class	Mains suppression — replace if RIFA-branded

The spindle motor rail on a 5114 may be 12 V or 24 V depending on which 8-inch drive vendor is installed (Shugart, Memorex, etc.). Verify with a multimeter before ordering capacitor replacements.

Mains Suppression Capacitor

Same caveat as the IBM 5100 Capacitor Replacement Guide: RIFA-branded X2 capacitors on either the 5110 or 5114 PSU vent over time and emit a fish odour. Replace immediately as a preventive measure if RIFA-branded.

CRT Deflection / Flyback Board

Same as the IBM 5100 — the 5-inch CRT and its deflection board are common between 5100 and 5110. Refer to the IBM 5100 Capacitor Replacement Guide for the deflection / flyback board cap list.

DC300 Tape Drive (Model 1)

Same as the IBM 5100 — refer to that page.

8-Inch Floppy Drive Logic Board Capacitors

The 8-inch floppy drives inside the 5114 carry their own logic board capacitors. Typical values for Shugart-class drives:

8-inch floppy drive logic board (representative)

Value	Voltage	Type	Position
47 µF	16 V	Aluminium electrolytic	Spindle motor driver
22 µF	16 V	Aluminium electrolytic	Sector buffer
10 µF	25 V	Aluminium electrolytic	Head amp
4.7 µF	16 V	Tantalum	IC bypass

If a drive becomes unreliable warm but stable cold, recap the drive logic board with 105 °C low-ESR equivalents.

ROS / RWS Card Capacitors

The Executable ROS, Language ROS, IEEE-488 controller card, RS-232 card, and RWS cards carry small tantalum decoupling caps. Same diagnostic procedure as the IBM 5100:

1. Multimeter on diode test.
2. Probe each tantalum in-circuit: black to ground, red to rail.
3. Good cap reads open / high resistance; shorted cap reads close to 0 Ω.
4. Remove and confirm.
5. Replace with tantalum or low-ESR ceramic of equal value, equal or higher voltage.

Recommended Modern Replacements

Same as the IBM 5100:

• Manufacturer: Panasonic FR/FM/FC, Nichicon HE/HZ (post-2007 date codes), Rubycon ZLH/ZLJ/YXJ, United Chemi-Con KZH/KZE. Avoid generic Chinese brands for PSU rebuild.
• 105 °C even where IBM original was 85 °C.
• Voltage equal or higher than original.
• Capacitance equal to original.
• Verify lead spacing — many originals are axial, modern replacements are typically radial.

Recap Procedure

1. Discharge the PSU bulk capacitors on both the 5110 and (if attached) the 5114.
2. Discharge the CRT anode before any deflection-board work.
3. Remove the PSU board(s) from the chassis.
4. Photograph from both sides at high resolution.
5. Desolder each electrolytic with solder wick. Limit each cycle to 5–7 seconds at no more than 350 °C.
6. Fit replacements matching silkscreen polarity.
7. Solder both leads; inspect for clean fillets; trim flush.
8. Reassemble.
9. Verify rails on the bench under a 1–2 A resistive load before refitting.

Post-Recap Verification

1. Power on the 5110 standalone (no 5114).
2. Verify rails at planar power connector.
3. Verify language banner appears clean.
4. Run Diagnostic ROS.
5. Power off; attach 5114; power on 5114.
6. Verify 5114 rails.
7. Run the Customer Acceptance Test from diskette.
8. Verify each 8-inch floppy drive reads and writes.

If any test fails, re-inspect cap polarity first.

Polarity Reference

Polarity reference for IBM motherboard tantalum and aluminium electrolytic capacitors. Match the silkscreen "−" to the cap stripe. (Image: minuszerodegrees.net)

When Not to Recap

If both the 5110 and any attached 5114 power on cleanly, all rails are within tolerance, the language banner is clean, and there is no visible cap failure, the caps are within tolerance. Given the machine's age, planned recap before any extended use is strongly recommended.

Always recap if:

• Any visible cap failure on either unit.
• PSU smoke, fishy odour or audible whine on either unit.
• Rails out of tolerance on either unit.
• RIFA-branded X2 mains suppression cap present (preventive replacement).
• 5114 drive becomes unreliable when warm.

Related Pages

• IBM 5110
• IBM 5110 Maintenance Guide
• IBM 5110 Troubleshooting Guide
• IBM 5100 Capacitor Replacement Guide — sibling machine
• IBM 5120 Capacitor Replacement Guide — sibling machine (5110 Model 3)
• Capacitor Failure Symptoms

References

• Bitsavers — IBM 5110 documents. MIM SY31-0550, 5114 MIM SY31-0551, Parts Catalog S131-0626.
• IBM 5110 — Wikipedia.
• Commonly Failing Electronic Components — minuszerodegrees.net.
• Stuttgart Computermuseum — IBM 5110. Community restoration notes.