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IBM PC Series 300 Capacitor Replacement Guide

From RetroTechCollection

This guide documents capacitor diagnosis and replacement for the IBM PC Series 300 family. The main subject is the CHHSI 560 µF / 25 V capacitor plague that affects the PC 300PL 6862 / 6892 boards — community-confirmed and well-documented on Badcaps.net. Earlier first-generation PC 300 boards (486 / Pentium era, before 1997) predate the capacitor plague and are generally healthy; later PC 300GL Celeron boards (6275 / 6285) sit at the edge of the plague window and warrant inspection.

Safety Warning

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All PC Series 300 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.

CHHSI Capacitor Plague (PC 300PL 6862 / 6892)

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The PC 300PL machine types 6862 and 6892 are community-confirmed victims of the CHHSI capacitor plague — a separate but contemporary failure mode to the better-known Nichicon HM / Rubycon MBZ plague that affects the IBM IntelliStation line.[1] Specific fault parts:

  • CHHSI brand low-ESR aluminium electrolytic capacitors.
  • 560 µF / 25 V rating.
  • WG(M) date code series (1998–1999 manufacture).
  • Located around the VRM and CPU power filtering on the 6862 / 6892 NLX planar.[2]

Community recap recommendation: replace every CHHSI cap on the board, regardless of whether it appears visually compromised — the failure mode includes silent ESR rise without visible bulging.

Detection

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  1. Power off, unplug, discharge.
  2. Remove the 6862 / 6892 NLX planar from the chassis (see IBM PC Series 300 Maintenance Guide).
  3. Inspect every electrolytic cap on the planar with a USB microscope or magnifier:
    • CHHSI-branded caps with WG(M) date codes — recap regardless of appearance.
    • Visibly bulged tops, leaked electrolyte, discolouration around the base — recap immediately.
  4. Measure ESR with an in-circuit ESR meter (Bob Parker MK-328 etc.) if available.

CHHSI Replacement

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Recommended modern post-plague replacements (in order of preference):

  • Panasonic FR / FM — high-grade Japanese low-ESR.
  • Nichicon HE / HZ (post-2007 date codes only) — Nichicon's post-plague line.
  • Rubycon ZLH / ZLJ / YXJ — Rubycon's post-MBZ replacement.
  • United Chemi-Con KZH / KZE — Japanese low-ESR.
  • Polymer alternatives (Panasonic FP, Nichicon LE) — drop-in for the 25 V VRM positions where through-hole space permits.

Do not substitute general-purpose 85 °C / 105 °C caps for low-ESR types — the VRM ripple will exceed the cap's tolerance and the new caps will fail within months.

Replacement Procedure

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  1. Photograph the planar at high resolution from both sides. Record every cap's location, value, polarity, lead spacing.
  2. Remove the planar from the chassis.
  3. For each CHHSI cap:
    1. Apply fresh solder + flux to both leads from the underside.
    2. Heat both leads alternately while pulling the cap from the top side.
    3. Clean both holes with solder wick.
    4. Insert the new cap matching the silkscreen polarity (− on cap stripe to − silkscreen mark).
    5. Solder both leads from the underside. Inspect for a clean fillet.
    6. Trim leads flush.
  4. Use a temperature-controlled iron at no more than 350 °C; limit each desolder cycle to 5–7 seconds.

The 6862 / 6892 planar is multilayer with thermal vias on the ground side — be patient on the VRM ground-side caps.

PC 300PL 6862 / 6892 Cap List (Representative)

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PC 300PL 6862 / 6892 planar capacitor replacement (representative)
Value Voltage Type Position Quantity (approx)
560 µF 25 V Low-ESR aluminium, 105 °C — CHHSI plague position CPU VRM / power filtering 4–6
470 µF 16 V Low-ESR aluminium, 105 °C Memory subsystem / AGP slot 2–3
220 µF 16 V Low-ESR aluminium, 105 °C Southbridge / I/O 4
100 µF 16 V Aluminium electrolytic, 105 °C Misc decoupling 6
47 µF 16 V Aluminium electrolytic +5 VSB 1

The 560 µF / 25 V CHHSI position is the headline failure; the lower-value caps are inspected during the same recap but rarely require replacement.

PC 300GL Celeron 6275 / 6285 Caps

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The Celeron 6275 / 6285 (440BX, Celeron PPGA) is at the edge of the plague window. CHHSI was not the dominant cap brand on this board — community reports are mixed. Inspect every electrolytic and recap only if:

  • Bulged or leaked caps visible.
  • System unstable under sustained load.
  • Date codes are 1998–1999 and brand is on the suspect list (CHHSI, Lelon, GSC, CapXon, Taicon).

PC 300XL 6588 Caps

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The 6588 (440FX, Pentium MMX / II Klamath) predates the plague (1996–1997 production) and is rarely affected. Inspect for bulged caps anyway as a precaution.

First-Generation (PC 300 Series Models 330–350) Caps

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The 6571 / 6573 / 6575 / 6576 / 6577 / 6581 / 6583 / 6585 / 6586 / 6587 boards predate the plague (1995–1996 production). Planar electrolytics are mostly through-hole 100–470 µF in the +5 V and +12 V power input area, plus tantalum decoupling around the CPU and chipset. Failures are rare but possible after 25+ years.

Representative first-generation cap list:

First-generation PC 300 planar capacitor list (representative)
Value Voltage Type Position Quantity (approx)
10 µF 16 V Tantalum IC bypass around CPU, video, chipset ~10–20
22 µF 16 V Tantalum Memory bank decoupling ~4–6
100 µF 16 V Aluminium electrolytic, 105 °C low-ESR Power input filtering 2–3
220 µF 16 V Aluminium electrolytic, 105 °C low-ESR Power input filtering 1–2
470 µF 16 V Aluminium electrolytic, 105 °C low-ESR Bulk filter near power connector 1–2

PC 365 6589 Caps (Dual Pentium Pro)

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The dual-Pentium Pro 6589 carries a larger VRM than other PC 300 boards (Socket 8 Pentium Pro at 200 MHz draws ~35 W per CPU). Representative cap layout:

PC 365 6589 planar cap list (representative)
Value Voltage Type Position
1500 µF 6.3 V Low-ESR aluminium, 105 °C CPU 0 / CPU 1 VRM output × 4–6
1000 µF 6.3 V Low-ESR aluminium, 105 °C CPU VRM phase output
470 µF 16 V Low-ESR aluminium, 105 °C +12 V VRM input
220 µF 16 V Low-ESR aluminium, 105 °C Southbridge / I/O
100 µF 16 V Aluminium electrolytic, 105 °C Misc decoupling

PSU Recap

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PC Series 300 PSUs are standard ATX (early) or NLX (late) form factor. Common topology:

  • Primary side — bridge rectifier, X2 mains suppression cap, 220 µF / 200 V (early) or 470 µF / 200 V (NLX) primary bulk, switching transistor, switching transformer.
  • Secondary side — rectifier diodes, low-ESR smoothing electrolytics, output chokes, optocoupler feedback.
PC Series 300 PSU capacitor replacement summary (typical 145–230 W ATX / NLX)
Value Voltage Type Typical position
3300 µF 6.3 V Low-ESR aluminium, 105 °C +3.3 V smoothing × 2 (NLX / Pentium II / III generation)
2200 µF 16 V Low-ESR aluminium, 105 °C +5 V smoothing × 2
2200 µF 25 V Low-ESR aluminium, 105 °C +12 V smoothing × 1
1000 µF 35 V Low-ESR aluminium, 105 °C +12 V auxiliary
470 µF 16 V Aluminium electrolytic, 105 °C +5 VSB smoothing
220 µF 35 V Aluminium electrolytic, 105 °C −12 V smoothing
100 µF 50 V Aluminium electrolytic, 105 °C Primary auxiliary
47 µF 50 V Aluminium electrolytic, 105 °C Primary startup
470 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

A common PSU failure on the 300PL 6862 / 6892 is +5 VSB regulator cap failure — the 47 µF / 16 V cap on the standby flyback secondary leaks or shorts, causing:

  • Green standby LED dim or off.
  • Wake-on-LAN non-functional.
  • System refuses to power on from the front-panel button.

Replace with a 105 °C low-ESR equivalent.

Recap Procedure

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  1. Discharge the bulk capacitor; verify with a multimeter.
  2. Remove the PSU from the chassis (4 screws typically; the NLX PSU on 300PL slides out from the rear).
  3. Open the PSU housing.
  4. Photograph the board. Mark each electrolytic's polarity.
  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 2 A resistive load before refitting to the chassis.

Graphics Card Capacitors

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The optional add-in graphics cards available on PC 300PL boards (Matrox MGA-G200 / G400, ATI Rage Pro NLX, NVIDIA TNT2 M64 32 MB, S3 Savage4) carry SMD ceramic + tantalum decoupling around the GPU and VRAM.

Failure mode: tantalum short circuit. Symptoms:

  • System will not POST with the card installed but POSTs when card removed.
  • Card heats up unevenly with hot spot near a specific tantalum.
  • PSU +5 V or +3.3 V rail sags when the card is inserted.

Diagnosis:

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

Drive Logic Board Capacitors

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Original IBM Deskstar DTLA / IC35L drives from the PC 300 era carry aluminium electrolytics on the drive logic board. Typical values:

  • 47 µF / 16 V — spindle motor driver.
  • 10 µF / 25 V — head amp.
  • 22 µF / 16 V — sector buffer.

Modern alternative: replace the original IDE drive with a CompactFlash-to-IDE or DOM (Disk-on-Module) adapter — no recap needed, fast, reliable.

Replacement Parts Summary

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PC Series 300 system-wide cap replacement summary
Value Voltage Type Where
10 µF 16 V Tantalum or low-ESR SMD First-generation planar IC bypass
22 µF 16 V Tantalum or low-ESR SMD Memory bank decoupling, drive sector buffer
47 µF 16 V Aluminium electrolytic, 105 °C low-ESR +5 VSB filter, drive motor driver
100 µF 16 V Aluminium electrolytic, 105 °C Planar misc decoupling
220 µF 16 V / 35 V Aluminium electrolytic, 105 °C Planar power input / PSU −12 V
470 µF 16 V / 35 V Aluminium electrolytic, 105 °C low-ESR Planar bulk filter / PSU +12 V auxiliary
560 µF 25 V Low-ESR aluminium, 105 °C PC 300PL 6862 / 6892 CHHSI plague position — primary recap target
1000 µF 6.3 V / 16 V Low-ESR aluminium, 105 °C PC 365 6589 VRM, PSU +5 V auxiliary
1500 µF 6.3 V Low-ESR aluminium, 105 °C PC 365 6589 VRM output
2200 µF 16 V / 25 V Low-ESR aluminium, 105 °C PSU +5 V / +12 V smoothing
3300 µF 6.3 V Low-ESR aluminium, 105 °C NLX PSU +3.3 V smoothing
47 µF 50 V Aluminium electrolytic, 105 °C PSU primary startup
470 µF 200 V Aluminium electrolytic, 105 °C PSU primary bulk (lethal-charge component)
0.1 µF 275 VAC X2 class PSU mains suppression

Polarity Reference

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The PC Series 300 planar silkscreen marks the negative side of each electrolytic with a darkened half-circle or stripe. The cap body shows the negative side with a stripe and "−". Match these conventions.

Polarity reference for IBM motherboard tantalum and aluminium electrolytic capacitors. Match the silkscreen "−" to the cap stripe. (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; observe IBM SurePath splash and POST.
  4. Press F1 during SurePath splash to enter Setup; verify memory size, drive types.
  5. Run Memtest86+ for a full memory pass.
  6. Boot the OS; run a sustained CPU + disk + GPU load (e.g. POV-Ray under Windows, Prime95) for several hours.

If the system was previously failing under load and now passes, the recap was successful.

If any test fails after 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 PC Series 300 boots, POSTs cleanly, runs reliably under sustained load with no errors and visual inspection shows no cap failure, the caps are within tolerance.

Always recap if:

  • Any CHHSI cap visible on a PC 300PL 6862 / 6892 (regardless of visual condition).
  • Visible cap failure (bulged top, leaked electrolyte) on any PC 300 board.
  • PSU smoke, fishy odour or audible whine.
  • System unstable under load, random reboots, fails to leave standby.
  • Wake-on-LAN non-functional on 300PL (typically +5 VSB cap failure).
  • System unstable when warm but stable when cold.
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References

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  1. ↑ https://en.wikipedia.org/wiki/Capacitor_plague
  2. ↑ https://www.badcaps.net/forum/troubleshooting-hardware-devices-and-electronics-theory/troubleshooting-desktop-motherboards-graphics-cards-and-pc-peripherals/86515-ibm-300pl
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