Josh: Split combined PS/2 50/60 and 70/80 pages into per-model pages

2026-05-22T09:46:19Z

Split combined PS/2 50/60 and 70/80 pages into per-model pages

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This guide documents capacitor diagnosis and replacement for the '''[[IBM PS/2 Model 70]]''' (machine type 8570, all submodels), covering the planar, the 132 W PSU, the IBM ESDI Fixed Disk Adapter/A, the floppy and ESDI drive logic boards, and the Power Platform daughtercard (8570-B21 / B61).

The Model 70 planar is one of the two most famously-leaky PS/2 planars (the other being the Model 80). The '''surface-mount aluminium electrolytic''' capacitors on the planar are the defining failure mode of the system and the primary subject of this guide.

== Safety Warning ==

The 132 W PSU contains mains-rectified bulk capacitors that hold a lethal charge after power-off. Before any PSU work:

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

No CRT in the system unit.

== The SMD Electrolyte Plague ==

The Model 70 planar (and the Model 80 planar) carries surface-mount aluminium electrolytic capacitors — typically '''10 µF / 16 V''' and '''47 µF / 16 V''' — scattered across both sides of the planar for IC supply rail bypassing. After 30+ years the rubber bung seal at the base of these SMD caps degrades and the corrosive aluminium electrolyte leaks onto the planar.

=== How the Leak Damages the Planar ===

The leaked electrolyte is mildly conductive (causing intermittent shorts on adjacent traces) and is corrosive (eating through copper traces and IC pins). The damage progresses on the following timeline once leakage starts:

# Mild discolouration of the solder mask near the cap base (months).
# Crusty deposits forming on adjacent vias and traces (1–2 years).
# First intermittent POST faults — system passes cold, fails warm (2–3 years from start of leak).
# Permanent loss of specific functional blocks (VGA, RTC, MCA bus controller) as traces corrode through (3–5 years).
# Dead planar with corroded traces and lifted pads requiring extensive board-level repair (5+ years).

The leakage continues at room temperature with no power applied. '''Storage in a damp environment accelerates the damage.'''

=== Detection ===

# Power off, unplug, discharge PSU.
# Remove the planar from the chassis floor.
# Inspect both sides under a USB microscope or magnifier with bright lighting. Look for:
#* Brown or green residue near a SMD cap base.
#* Discolouration of solder mask.
#* Crusty deposits on adjacent vias.
#* Lifted SMD cap (one end of the cap raised from the pad).
#* Cracked solder mask near a cap.
#* Any "fishy" smell from the planar.
# Photograph every cap location for reference before any work.

If '''any''' SMD cap shows leakage, all of them should be replaced — the rest are at the same age and will leak within a few years.

=== Replacement Procedure ===

# Photograph the planar from both sides at high resolution. Record every cap's location, value (top marking) and orientation.
# Remove every SMD electrolytic with a hot-air rework station (set to 320 °C, 30 seconds per cap). Lift each cap straight up; do not pry sideways or you may lift pads.
# Clean each pad with solder wick.
# Wash the planar with isopropyl alcohol (90%+) and a soft brush. For severely contaminated planars, an ultrasonic cleaner (with planar-safe detergent) is the best option. Dry thoroughly (compressed air or a low-temp oven; ensure all moisture is gone before any rework).
# Inspect every pad for damage. Where pads are lifted or traces corroded through, repair with 30 AWG enamelled wire or with a UV-cure trace repair kit.
# Fit replacements: use '''through-hole 10 µF / 16 V''' tantalum (preferred) or '''SMD low-ESR aluminium 10 µF / 16 V''' or '''through-hole 47 µF / 16 V''' equivalents. Many restorers prefer to substitute through-hole tantalum for SMD aluminium because tantalum does not leak (though tantalum has its own failure mode — short circuit if exceeded on voltage).
# Verify polarity on every cap before soldering.

=== Capacitor Locations on the Planar ===

The Model 70 planar carries approximately '''36–40 SMD electrolytics''' in total (count varies by planar revision). Common locations:

* Near the 80386DX socket — '''10 µF / 16 V''' bypass.
* Near the VGA chip and VRAM — '''10 µF / 16 V''' bypass × 4–6.
* Near the SIMM sockets — '''47 µF / 16 V''' bulk × 2.
* Near the MCA bus controller — '''10 µF / 16 V''' bypass × 2–3.
* Near the floppy controller — '''10 µF / 16 V''' bypass × 1–2.
* Near the RTC (DS1287) — '''10 µF / 16 V''' bypass × 1.
* Near the power-input filter — '''47 µF / 16 V''' bulk × 2.

== Planar Capacitors Summary ==

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Model 70 planar SMD electrolytic replacement summary'''
! Value !! Voltage !! Type !! Quantity !! Notes
|-
| 10 µF || 16 V || SMD aluminium (original) → tantalum / SMD low-ESR replacement || ~30 || IC bypass throughout
|-
| 47 µF || 16 V || SMD aluminium (original) → tantalum / SMD low-ESR replacement || ~6–10 || Bulk filtering near SIMM sockets and power input
|-
| 22 µF || 16 V || SMD aluminium (original) → SMD low-ESR replacement || ~2–4 || On some planar revisions
|}

The exact count depends on planar revision. Inspect every SMD electrolytic on the planar before ordering replacements.

== 132 W PSU Recap ==

The Model 70 132 W PSU is a single-board switching supply. Common cap values:

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Model 70 132 W PSU capacitor replacement summary'''
! Value !! Voltage !! Type !! Typical position !! Notes
|-
| 2200 µF || 16 V || Low-ESR aluminium electrolytic, 105 °C || +5 V smoothing × 2 || Critical for +5 V stability
|-
| 1000 µF || 16 V || Low-ESR aluminium electrolytic, 105 °C || +5 V auxiliary × 1 ||
|-
| 470 µF || 35 V || Low-ESR aluminium electrolytic, 105 °C || +12 V smoothing × 1 || Drive motor rail
|-
| 220 µF || 35 V || Aluminium electrolytic, 105 °C || −12 V smoothing × 1 ||
|-
| 100 µF || 50 V || Aluminium electrolytic, 105 °C || Primary auxiliary × 2 ||
|-
| 100 µF || 16 V || Aluminium electrolytic, 105 °C || Bypass / feedback × 2–3 ||
|-
| 47 µF || 50 V || Aluminium electrolytic, 105 °C || Primary startup × 1 ||
|-
| 220 µF || 200 V || Aluminium electrolytic, 105 °C || Primary bulk × 1 || Lethal charge — discharge before work
|-
| 0.1 µF || 275 VAC || X2 class || Mains suppression × 1 || Replace if RIFA-branded
|}

=== Recap Procedure ===

# Discharge the bulk capacitor; verify with a multimeter.
# Remove the PSU from the chassis (4 screws).
# Open the PSU housing. The Model 70 PSU shell is normally screwed.
# Photograph the board. Mark each electrolytic's polarity.
# Desolder each electrolytic with solder wick on each lead.
# Fit '''low-ESR''', '''105 °C''' replacements, equal capacitance, equal or higher voltage rating.
# Inspect the X2 mains suppression cap. If RIFA-branded or cracked / bulging, replace.
# Reassemble. Verify rails on the bench with a multimeter under a 1 A resistive load before refitting to the chassis.

== ESDI Fixed Disk Adapter/A Capacitors ==

The IBM ESDI Fixed Disk Adapter/A drives the 60 / 120 MB ESDI hard drive. Cap values are the same as on the Model 50 / 60 ESDI controller:

* '''10 µF / 16 V''' (multiple positions) — IC bypassing.
* '''22 µF / 16 V''' (one or two positions) — sector buffer power.
* '''47 µF / 16 V''' (one position) — on-card 5 V regulation.

If the ESDI controller reports a 10455 or 10463 on a known-good drive, recap the controller card capacitors before condemning the card.

== ESDI Drive Logic Board ==

The 60 / 120 MB ESDI drives carry their own drive logic board with aluminium electrolytics. Typical values:

* '''47 µF / 16 V''' — near the spindle motor driver.
* '''10 µF / 25 V''' — near the head-amp section.
* '''22 µF / 16 V''' — sector buffer.

Symptoms of aged drive caps include the drive not spinning up reliably, CRC errors on reads, and the drive becoming unreliable when warm.

== Floppy Drive Logic Board ==

Same as Model 50 / 60. The PS/2 1.44 MB floppy drives carry '''47 µF / 16 V''' (motor driver) and '''10 µF / 25 V''' (head amplifier) electrolytics. Recap with 105 °C low-ESR equivalents. The Mitsubishi MF355C family also needs a 54 × 1 mm flat rubber drive belt at the same time.

== Power Platform Daughtercard Capacitors (8570-B21 / B61) ==

The Power Platform 80486 daughtercard carries its own +5 V regulator and a small number of decoupling caps. Typical values:

* '''10 µF / 16 V''' tantalum × 4–6 — IC bypass around the 80486.
* '''47 µF / 16 V''' aluminium electrolytic × 1 — +5 V smoothing on the regulator output.
* '''22 µF / 16 V''' tantalum × 2 — clock generator bypass.

If a Power Platform-equipped Model 70 fails to POST or shows 80486-specific faults, inspect the daughtercard for cap leakage and recap if needed.

== Replacement Parts Summary ==

{| class="wikitable styled-table" style="width:100%; text-align:center;"
|+'''Model 70 system-wide cap replacement summary'''
! Value !! Voltage !! Type !! Where
|-
| 10 µF || 16 V || Tantalum (preferred) or SMD low-ESR || Planar SMD positions, ESDI / Power Platform card bypass
|-
| 22 µF || 16 V || Tantalum or SMD low-ESR || Planar SMD on some revisions, ESDI sector buffer, Power Platform clock generator
|-
| 47 µF || 16 V || Tantalum or SMD low-ESR || Planar SMD bulk, drive logic board, Power Platform regulator output
|-
| 100 µF || 16 V || Aluminium electrolytic, low-ESR, 105 °C || PSU bypass / feedback
|-
| 220 µF || 35 V || Aluminium electrolytic, 105 °C || PSU −12 V smoothing
|-
| 220 µF || 200 V || Aluminium electrolytic, 105 °C || PSU primary bulk (lethal-charge component)
|-
| 470 µF || 35 V || Low-ESR aluminium electrolytic, 105 °C || PSU +12 V smoothing
|-
| 1000 µF || 16 V || Low-ESR aluminium electrolytic, 105 °C || PSU +5 V auxiliary
|-
| 2200 µF || 16 V || Low-ESR aluminium electrolytic, 105 °C || PSU +5 V smoothing × 2
|-
| 0.1 µF || 275 VAC || X2 class || PSU mains suppression
|-
| 100 µF || 50 V || Aluminium electrolytic, 105 °C || PSU primary auxiliary
|-
| 47 µF || 50 V || Aluminium electrolytic, 105 °C || PSU primary startup
|}

== Polarity Reference ==

[[File:IBM 5150 tantalum polarity reference.jpg|center|thumb|640px|Polarity reference for IBM motherboard tantalum capacitors. The convention applies to the Model 70 planar SMD positions when fitting tantalum replacements. (Image: minuszerodegrees.net)]]

A failed tantalum often shows '''no visible damage'''.

[[File:IBM 5150 failed tantalum visual example.jpg|right|thumb|300px|Failed tantalum on an IBM motherboard. (Image: minuszerodegrees.net)]]

== Post-Recap Verification ==

# Bench-test the planar with a known-good PSU and no peripherals.
# Verify rails at the planar power connector.
# Refit; boot the Reference Diskette.
# Run Auto Configuration if any MCA cards changed.
# Run Advanced Diagnostics (Ctrl-A) and walk through each test, paying special attention to:
#* Protected-mode test (104-class fault → SMD cap near CPU).
#* Memory test (full pass).
#* Onboard VGA test.
#* ESDI controller test.
# Run a memory test pass for several hours under DOS to confirm planar memory reliability.

If any test fails after a recap, re-inspect the polarity of every replaced cap before suspecting another fault — reversed polarity is the most common error.

== When Not to Recap ==

If the Model 70 boots, POSTs cleanly and runs reliably with no diagnostic errors '''and''' visual inspection shows no SMD leakage, the caps are within tolerance and continued use is acceptable. However, on a 30+ year old Model 70, this combination is increasingly rare; most surviving 8570s either have visible SMD leakage or are showing the first intermittent faults of impending leakage.

Always recap if:
* '''Any''' SMD electrolyte leak visible on the planar.
* Fluid leak visible from any electrolytic in the PSU or drive logic boards.
* PSU smoke, fishy odour or audible whine.
* ESDI controller reports 10455 / 10463 on a known-good drive.
* Drive becomes unreliable when warm.
* System passes POST cold but fails when warm.

== Related Pages ==

* [[IBM PS/2 Model 70]]
* [[IBM PS/2 Model 70 Maintenance Guide]]
* [[IBM PS/2 Model 70 Troubleshooting Guide]]
* [[IBM PS/2 Model 80 Capacitor Replacement Guide]] — tower sibling, same planar family of SMD electrolytics
* [[Capacitor Failure Symptoms]]

== References ==

* [https://www.minuszerodegrees.net/failure/failure.htm Commonly Failing Electronic Components], minuszerodegrees.net. Reference for SMD aluminium electrolyte leakage on the Model 70 / 80 planars.
* [https://www.dosdays.co.uk/computers/IBM%20PS2%20Model%2070/ibm_ps2_model_70.php IBM PS/2 Model 70 — DOS Days]. Reference for the 132 W PSU rating and ESDI controller architecture.
* [https://www.ardent-tool.com/qtechinfo/GJAN-43VS3S.html IBM PS/2 Model 70 — Ardent Tool Quick Reference]. FRU breakdown.
* IBM, ''IBM Personal System/2 Hardware Maintenance Manual'' (S52G-9971-02, October 1994).

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IBM PS/2 Model 70 Capacitor Replacement Guide - Revision history

Josh: Split combined PS/2 50/60 and 70/80 pages into per-model pages