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IBM PS/2 Model 60 Maintenance Guide

From RetroTechCollection

This guide documents preventive maintenance for the IBM PS/2 Model 60 (machine type 8560), a floor-standing tower with eight MCA expansion slots, four drive bays and a 207 W or 225 W PSU. The Model 60 chassis is the same tower used by the IBM PS/2 Model 80; most chassis procedures apply equally to both.

Safety Warning

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The Model 60 PSU (207 W on the 8560-041 or 225 W on the 8560-071) contains mains-rectified bulk capacitors that hold a lethal charge after power-off. Before any work inside the PSU shell:

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

There is no CRT in the system unit (matching IBM 8503 / 8512 / 8513 / 8514 displays are serviced separately).

Opening the Tower Chassis

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Tools: Philips #2 screwdriver, T15 Torx (some Model 60 fasteners), anti-static strap.

  1. Power off and unplug all cables.
  2. Loosen the screws at the rear top edge of the tower.
  3. The larger of the two side panels slides off (left side, when looking at the front).
  4. Inside:
    • Planar mounts on the floor of the chassis.
    • MCA cards plug into the riser on the left side, accessed through the side panel.
    • Drive cage runs vertically up the front of the tower, with the four drive bays stacked.
    • PSU sits at the top of the chassis (above the drive cage).

The 21.3 kg weight makes the Model 60 unwieldy on a bench. Many restorers tip the tower on its side onto a soft surface for easier access to the MCA riser.

Drive Cage Layout

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The Model 60 has four drive bays:

  • Top bay: 5.25" full-height (often used for tape backup or a second 5.25" device).
  • Bay 2: 3.5" half-height (originally the 1.44 MB floppy).
  • Bay 3: 3.5" half-height (originally the hard drive on 8560-041 / 071).
  • Bay 4: 3.5" half-height spare.

Each bay accepts the IBM proprietary plastic drive sled with captive push-pin tabs. The sleds are released by pressing the plastic tabs inward with the IBM "crowbar" plastic spudger that shipped with the system.

Regular Cleaning

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  • Soft brush and low-pressure compressed air for the planar, MCA cards, drive bays and PSU vents.
  • Avoid blowing dust into the PSU fan bearing or onto the floppy heads.
  • Clean MCA card edge fingers with a soft eraser or a deoxidising contact cleaner before reseating. MCA contacts oxidise after 30+ years and produce intermittent card-not-detected (POST 165) symptoms.
  • Clean PS/2 keyboard and mouse Mini-DIN-6 connectors with deoxidising contact cleaner on a foam swab.
  • Inspect the planar for any leaked electrolyte around through-hole electrolytics. The Model 60 planar is less affected than the Model 70 / 80 by SMD electrolyte leakage but through-hole caps still age.

PSU Voltage Checks

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Probe the PSU output rails at the planar power connector with a multimeter.

Model 60 PSU rail tolerances
Rail Acceptable range
+5 V +4.75 V to +5.25 V
+12 V +11.4 V to +12.6 V
−5 V −4.75 V to −5.25 V
−12 V −11.4 V to −12.6 V

The 207 W PSU (8560-041) is sufficient for an ST-506-equipped Model 60. The 225 W PSU (8560-071) is uprated for the higher-current ESDI drive. Both PSUs auto-restart on power recovery.

The Model 60 PSU is electrically compatible with the IBM PS/2 Model 80 PSU in the same chassis. The Model 50 PSU is NOT a drop-in (different planar connector).

CMOS / RTC Battery

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Early Model 60 production units use a Motorola MC146818 RTC on the planar with a discrete external 4ร—AA battery pack (or 3 V lithium pack) feeding the planar via a 4-pin header. Later production units adopted the Dallas DS1287 / DS12887 integrated module on the planar (same as Model 50 / 50 Z).

Symptoms of a dead battery (either generation):

  • 161 โ€” CMOS configuration empty.
  • 162 โ€” CMOS checksum mismatch.
  • 163 โ€” Time and date not set.

Replacement procedure for the external pack:

  1. Power off; discharge PSU bulk capacitor.
  2. Locate the battery pack (typically secured to the chassis with adhesive backing or a plastic clip).
  3. Disconnect the 4-pin header.
  4. Fit a fresh 3 V lithium pack (e.g. modern Tadiran 3.6 V or 3 V CR2032 + 2 holder pack) with the correct polarity.

For the DS1287 / DS12887 module (later units):

  1. Power off; discharge PSU bulk capacitor.
  2. Identify the 24-pin DIP marked "DALLAS" on the planar.
  3. Desolder using solder wick and a fine-tipped iron at no more than 350 ยฐC.
  4. Fit a fresh Dallas DS12887+ or a socket for future replacements.
  5. Reassemble; boot Reference Diskette; run SETUP.

MCA Card Maintenance

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Each MCA card has a unique ID stored in the card itself. The Reference Diskette reads the ID, looks up the ADF (Adapter Definition File) and configures interrupts, DMA and memory addresses. After any card change:

  1. Boot the Reference Diskette.
  2. Select Set Configuration โ†’ Run Auto Configuration.
  3. Insert each option diskette as prompted to load missing ADFs.

Without Auto Configuration, the system reports a 165 card-ID-mismatch error at POST.

ESDI Drive Maintenance (8560-071)

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The 70 MB ESDI drive on the 8560-071 plugs directly into the IBM ESDI Fixed Disk Adapter/A on the MCA bus.

Common faults:

  • Drive stiction โ€” drive does not spin up after long storage. Rotate the drive case gently while powered off; reinstall; spindle frees for one boot. Image the contents immediately and replace.
  • Aged drive electrolytics โ€” brown crust around drive logic board caps. Recap with 105 ยฐC low-ESR equivalents.
  • Slow startup โ€” aged spindle motor bearings or drive PSU caps. Drive replacement is the practical fix.

ST-506 Drive Maintenance (8560-041)

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The 44 MB ST-506 drive on the 8560-041 plugs into the IBM Fixed Disk Adapter/A. ST-506 drives in PS/2 service are not the same Seagate ST-506 as in the IBM AT โ€” they are PS/2-specific drives with the proprietary single-cable interface.

Common faults are similar to the ESDI but with ST-506-specific 1701 / 1780 codes. See IBM PS/2 Model 60 Troubleshooting Guide.

Floppy Drive Maintenance

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Same as Model 50. 1.44 MB 3.5" half-height. Belt and drive-logic-board recap as in IBM PS/2 Model 60 Capacitor Replacement Guide.

Connector Care

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  • PS/2 keyboard / mouse: Mini-DIN-6 with plastic alignment key.
  • Keyboard / mouse fuse (3 A) on the planar protects the +5 V to keyboard and pointing device.
  • Serial (DB-25 male) and parallel (DB-25 female).
  • MCA edge connectors โ€” clean cards and slots before any work.

Capacitor Health

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Tantalum and aluminium electrolytic capacitors on the Model 60 planar, the PSU and the drive logic boards age and should be inspected. Full procedure: IBM PS/2 Model 60 Capacitor Replacement Guide.

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  • Philips #2 screwdriver and T15 Torx.
  • Anti-static strap.
  • Digital multimeter.
  • Plastic crowbar / spudger for captive push-pin tabs.
  • IPA + foam swabs.
  • Reference Diskette + ADF diskettes for all fitted MCA cards.
  • Spare Dallas DS12887+ for RTC replacement, or 3 V lithium pack for early-production external battery.
  • Soldering iron with fine tip + solder wick.
  • Drive belt (54 ร— 1 mm flat) for the Mitsubishi MF355C floppy.
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References

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