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IBM RS/6000 Capacitor Replacement Guide

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This guide documents capacitor diagnosis and replacement for the IBM RS/6000 family, covering the planar, the PSU, the IBM POWER GXT graphics cards, NVRAM TimeKeeper modules, and the drive and CD-ROM logic boards. RS/6000 capacitor topology varies significantly between eras — the Micro Channel POWER1 / POWER2 7012 and 7013 planars carry the same generation of surface-mount aluminium electrolytic capacitors that afflict the IBM PS/2 Model 70 / IBM PS/2 Model 80 planars (the "PS/2 plague"), while the later CHRP / PCI machines (7025 / 7026 / 7043 / 7044) use through-hole tantalum and through-hole aluminium electrolytics that age more slowly.

Safety Warning

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All RS/6000 PSUs contain mains-rectified bulk capacitors that hold a lethal charge after power-off. Before any PSU work:

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

Rack-class RS/6000s (7015, 7026 H-series) may carry dual or redundant PSUs and may be wired to −48 V DC instead of mains. Confirm the input topology before any service work.

Era Summary

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RS/6000 planar capacitor topology by era
Era Machine types Planar caps Failure mode
POWER1 / POWER2 Micro Channel 7011, 7012, 7013, 7015 SMD aluminium electrolytic + through-hole tantalum SMD electrolyte leakage (same generation as PS/2 70/80)
PReP / Carolina 7248 Through-hole tantalum + small SMD ceramic Tantalum short circuit
CHRP / PCI 7025, 7026, 7043, 7044 Through-hole aluminium + SMD ceramic + tantalum Aged secondary electrolytics in PSU; tantalum decoupling failure on graphics cards

7012 / 7013 Planar SMD Electrolyte Leak — Primary Failure Mode

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The POWER1 / POWER2 era 7012 and 7013 planars carry 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. The aluminium electrolyte inside these caps is corrosive and the rubber bung seal degrades over decades, allowing the electrolyte to leak onto the planar.

Failure Progression

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Identical to the PS/2 Model 70 / 80 plague:

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

Detection

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  1. Power off, unplug, discharge PSU.
  2. Remove the planar from the chassis.
  3. Inspect both sides under a USB microscope or bright light.
  4. Look for brown / green residue near any SMD electrolytic cap, discolouration of solder mask, crusty deposits on adjacent vias, lifted pads or corroded traces, "fishy" electrolyte smell.

If any SMD cap shows leakage, all of them should be replaced — they are all the same age.

Replacement Procedure

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Identical to the PS/2 70/80 procedure:

  1. Photograph the planar from both sides at high resolution. Record every cap's location, value (top marking), orientation.
  2. 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.
  3. Clean each pad with solder wick.
  4. Wash the planar with isopropyl alcohol (90%+). For severely contaminated planars, an ultrasonic cleaner with planar-safe detergent.
  5. Inspect every pad for damage. Repair lifted pads or corroded traces with 30 AWG enamelled wire.
  6. Fit replacements: through-hole 10 µF / 16 V tantalum (preferred) or SMD low-ESR aluminium 10 µF / 16 V; through-hole 47 µF / 16 V or equivalents.
  7. Verify polarity on every cap before soldering.
7012 / 7013 planar SMD electrolytic summary
Value Voltage Type Approx. quantity Notes
10 µF 16 V SMD aluminium (original) → tantalum / SMD low-ESR replacement 30–50 IC bypass throughout planar, near CPU MCM, near memory cards, near MCA bus controller
47 µF 16 V SMD aluminium (original) → tantalum / SMD low-ESR replacement 8–12 Bulk filtering near memory sockets and CPU MCM power input
22 µF 16 V SMD aluminium → SMD low-ESR replacement 2–4 Sector buffer / I/O bypass on some revisions

The exact count depends on planar revision. POWER2 39H/397/590/595 planars carry more caps than POWER1 320/530 planars because the MCM has more supply pins.

PSU Recap

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RS/6000 PSUs vary by machine type. Common topology: single-board switching supply with primary / secondary stages.

  • Primary side — bridge rectifier, X2 mains suppression cap, bulk capacitor (typically 220 µF / 200 V on smaller PSUs, 470 µF / 200 V on 7013 / 7015, 1000 µF / 250 V on H70 / H80 PSUs), switching transistor, switching transformer.
  • Secondary side — rectifier diodes, low-ESR smoothing electrolytics, output chokes, optocoupler feedback.

7012 / 7013 PSU Cap Values (Typical)

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7012 / 7013 PSU capacitor replacement summary (typical)
Value Voltage Type Typical position
2200 µF 16 V Low-ESR aluminium electrolytic, 105 °C +5 V smoothing × 2
2200 µF 25 V Low-ESR aluminium electrolytic, 105 °C +12 V smoothing
470 µF 35 V Aluminium electrolytic, 105 °C +12 V auxiliary
220 µF 35 V Aluminium electrolytic, 105 °C −12 V smoothing
100 µF 50 V Aluminium electrolytic, 105 °C Primary auxiliary
100 µF 16 V Aluminium electrolytic, 105 °C Bypass / feedback
47 µF 50 V Aluminium electrolytic, 105 °C Primary startup
470 µF 200 V Aluminium electrolytic, 105 °C Primary bulk × 1 (lethal-charge component)
0.1 µF 275 VAC X2 class Mains suppression — replace if RIFA-branded

The exact cap list per machine type is in the corresponding IBM service guide (SA38-0531 for 7013 500-series).[1]

7013 500-Series Fan-Sense Interlock

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A specific 7013 500-series PSU quirk: the supply refuses to stay on if it does not sense rotation of the cooling fan. Aged secondary electrolytics cause fan stutter at low duty cycle which causes the PSU to interpret a fan failure and shut down. Symptom: PSU runs for a few seconds, clicks, restarts in a loop. Recap fixes this.[2]

7043 / 7044 PSU Cap Values (Typical)

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The 7043 and 7044 PSUs have a 3.3 V rail added for the CPU and carry slightly more secondary filtering:

7043 / 7044 PSU capacitor replacement summary (typical)
Value Voltage Type Position
3300 µF 6.3 V Low-ESR aluminium electrolytic, 105 °C +3.3 V CPU rail smoothing × 1–2
2200 µF 16 V Low-ESR aluminium electrolytic, 105 °C +5 V smoothing × 2
2200 µF 25 V Low-ESR aluminium electrolytic, 105 °C +12 V smoothing
470 µF 35 V Aluminium electrolytic, 105 °C +12 V auxiliary
220 µF 35 V Aluminium electrolytic, 105 °C −12 V smoothing
100 µF 50 V Aluminium electrolytic, 105 °C Primary auxiliary
470 µF 200 V Aluminium electrolytic, 105 °C Primary bulk (lethal-charge component)
0.1 µF 275 VAC X2 class Mains suppression

7026-H70 750 W PSU

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The H70 PSU is FC 6290 (IBM PN 09P5429 / 24L0586).[3] It is a hot-swap unit; community-published cap lists exist but vary by revision — refer to the per-revision label on the PSU shell and the corresponding IBM service publication.

Recap Procedure (All PSUs)

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  1. Discharge the bulk capacitor; verify with a multimeter.
  2. Remove the PSU from the chassis.
  3. Open the PSU housing.
  4. Photograph the board. Mark each electrolytic's polarity with a paint pen.
  5. Desolder each electrolytic with solder wick.
  6. Fit low-ESR, 105 °C replacements, equal capacitance, equal or higher voltage rating.
  7. Inspect the X2 mains suppression cap. If RIFA-branded or cracked / bulging, replace.
  8. Reassemble. Verify rails on the bench with a multimeter under a 1 A resistive load before refitting to the chassis.

POWER GXT Graphics Card Capacitors

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The IBM POWER GXT family of graphics cards (GXT110P, GXT250P, GXT255P, GXT500P, GXT800P, GXT2000P, GXT3000P) all carry tantalum decoupling around the graphics chip and VRAM.

Common failure: GXT800P / GXT3000P tantalum decoupling short on the +5 V rail. Symptoms:

  • System will not POST with the card installed but POSTs when card removed.
  • GXT card heats up unevenly with hot spot near a specific tantalum cap.
  • PSU +5 V rail sags when the card is inserted.

Typical cap values on POWER GXT cards (representative):

  • 10 µF / 16 V tantalum × multiple — IC bypass around the graphics chip.
  • 22 µF / 16 V tantalum × 2–4 — VRAM bypass.
  • 47 µF / 16 V aluminium electrolytic × 1–2 — bulk filter near the PCI edge connector.

Diagnostic procedure:

  1. Set multimeter to diode test.
  2. Probe each tantalum in-circuit: black probe to ground, red probe to the rail side. Good cap reads as open / high resistance; failed (shorted) cap reads close to 0 Ω.
  3. Where a short is found, remove the cap to confirm.
  4. Replace with a fresh tantalum or low-ESR ceramic of equal value and equal or higher voltage rating.

NVRAM / RTC Module Replacement

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RS/6000 NVRAM / RTC modules are Dallas Semiconductor TimeKeeper parts with an internal lithium cell. The cell fails after 10–20 years.

Common Dallas parts in the family:

  • DS1287 / DS1287A — 24-pin DIP, same as PS/2 50/70/80.
  • DS1385 / DS1387 — DS1385 + integrated battery/crystal in an encapsulated module.
  • DS1644 — non-volatile TimeKeeping RAM.
  • DS1742W — 32-pin nonvolatile timekeeping RAM.
  • DS1746 / DS1746P — 128 KB × 8 NVSRAM + RTC, Y2K-compliant.

Replacement options:

  1. Fresh-date NOS or refurbished Dallas/Maxim part.
  2. Glitch Works GW-1742-1 (DS1742 substitute) — modern board with SRAM + RTC + CR1225 cell.[4]
  3. Glitch Works GW-1387-1 (DS1387 maintainable repair board).[5]
  4. Necroware nwX287 (DS12887 replacement using a CR1225 + modern SRAM + RTC chip).[6]
  5. DIY epoxy-case opening: cut the Dallas plastic case open, find the internal cell, replace with an external CR2032 holder.

Replacement procedure:

  1. Power off; discharge PSU bulk capacitor.
  2. Locate the Dallas DIP — typically near the RTC crystal or the boot ROM.
  3. Desolder using solder wick and a fine-tipped iron at no more than 350 °C; limit each cycle to 5–7 seconds.
  4. Fit a socket (recommended) before installing the replacement.
  5. Power on; enter SMS (F1 / F4); re-enter boot list, IP / SLIP config, date/time.

Drive Logic Board Capacitors

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Original IBM SCSI drives in long-running RS/6000s carry aluminium electrolytics on the drive logic board. 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. Recap with 105 °C low-ESR equivalents.

Modern alternative: replace the original SCSI drive with a SCSI2SD or BlueSCSI adapter (SD card → SCSI) — no recap needed; reliable; fast.

CD-ROM Drive Logic Board

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The SCSI CD-ROM drives shipped with 7043 / 7044 / 7025 / 7026 carry similar electrolytics on the drive logic board. Typical values:

  • 47 µF / 16 V — laser driver.
  • 100 µF / 6.3 V — sled motor driver.
  • 10 µF / 25 V — head amplifier.

Symptoms of aged CD-ROM caps include the drive refusing to eject, audio CD playback issues, and "media not ready" errors during AIX installation. Recap or replace with a modern SCSI CD-ROM.

Replacement Parts Summary

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RS/6000 family system-wide cap replacement summary
Value Voltage Type Where
10 µF 16 V Tantalum (preferred) or SMD low-ESR Planar SMD positions (7012 / 7013), GXT graphics card bypass
22 µF 16 V Tantalum or SMD low-ESR Planar SMD on some revisions, GXT VRAM bypass
47 µF 16 V Tantalum or SMD low-ESR Planar SMD bulk, drive logic board, GXT bulk
100 µF 6.3 V / 16 V Aluminium electrolytic, low-ESR, 105 °C CD-ROM sled motor, PSU feedback
100 µF 50 V Aluminium electrolytic, 105 °C PSU primary auxiliary
220 µF 35 V Aluminium electrolytic, 105 °C PSU −12 V smoothing
470 µF 35 V Aluminium electrolytic, 105 °C PSU +12 V auxiliary
470 µF 200 V Aluminium electrolytic, 105 °C PSU primary bulk (lethal-charge component)
2200 µF 16 V Low-ESR aluminium electrolytic, 105 °C PSU +5 V smoothing × 2
2200 µF 25 V Low-ESR aluminium electrolytic, 105 °C PSU +12 V smoothing
3300 µF 6.3 V Low-ESR aluminium electrolytic, 105 °C PSU +3.3 V CPU rail (7043 / 7044)
0.1 µF 275 VAC X2 class PSU mains suppression

Polarity Reference

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The RS/6000 planar silkscreen marks the + (positive, rail) side of each electrolytic with a small "+". The cap body shows the negative side with a stripe and "−". Match these conventions. The convention is the same as on the IBM PS/2 line.

 
Polarity reference for IBM motherboard tantalum capacitors. The convention applies to the RS/6000 planar SMD positions when fitting tantalum replacements. (Image: minuszerodegrees.net)

A failed tantalum often shows no visible damage.

 
Failed tantalum on an IBM motherboard. The small hole on the body is often the only visual indication. (Image: minuszerodegrees.net)

Post-Recap Verification

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  1. Bench-test the planar with a known-good PSU and no peripherals.
  2. Verify rails at the planar power connector.
  3. Refit; power on; watch the LED panel through BIST and IPL.
  4. Run AIX diag to verify all diagnostic categories pass.
  5. Run a memory test pass for several hours via AIX diag → Memory Test.
  6. Run a SCSI surface scan to confirm the storage subsystem is healthy after controller recap.

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

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If the RS/6000 boots, POSTs cleanly to AIX, errpt shows no hardware events, and the operator panel reaches the login prompt code (typically 551), the caps are within tolerance.

Always recap if:

  • Any SMD electrolyte leak visible on a 7012 / 7013 planar.
  • Fluid leak visible from any electrolytic in the PSU or drive logic boards.
  • PSU smoke, fishy odour or audible whine.
  • 7013 500-series PSU running in click-restart loop.
  • GXT graphics card pulling down +5 V or running hot.
  • Drive becomes unreliable when warm.
  • System passes BIST cold but fails when warm.
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References

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  1. ↑ https://www.ardent-tool.com/RS6000/docs/pdf/38053100.pdf
  2. ↑ https://www.ardent-tool.com/RS6000/docs/pdf/38053100.pdf
  3. ↑ https://www.amazon.com/IBM-6000-7026-H70-POWER-SUPPLY/dp/B000MRECHI
  4. ↑ https://www.tindie.com/products/glitchwrks/glitch-works-gw-1742-1-dallas-ds1742-replacement/
  5. ↑ https://www.tindie.com/products/glitchwrks/gw-1387-1-dallas-ds1387-maintainable-repair-board/
  6. ↑ https://github.com/necroware/nwX287
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