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SGI Power Series Capacitor Replacement Guide

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SGI Power-One SPM5 power supplies on the bench (jan-jaap)
Left, an SGI Power-One SPM5 from a Power Series or Crimson deskside with its output modules removed; right, a generic SPM5 kept for spares (jan-jaap)

Silicon Graphics published no capacitor values for the SGI Power Series, and no SGI service documentation for the range is available online.[1] The capacitor values known come from owners, chiefly jan-jaap, who rebuilt the power supplies of a 4D/380 rack and a 4D/440 deskside between 2022 and 2023.[2] The supplies themselves vary: This Old SGI lists LH Research, Cherokee, ACDC and Power-One units, mostly rated above 1000 W.[3] Check what is fitted to your own machine and record it before ordering parts.

Warning: in the Power-One SPM5, most of the input side is not isolated from the mains, the bias supply runs whenever the supply is connected, and about 70 V can remain on the main filter capacitors for more than ten minutes after power is removed. jan-jaap uses an isolated oscilloscope probe.[4]

Signs that the work is needed

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  • Leaked electrolyte in the output modules of a Power-One supply. jan-jaap found the 5 V module capacitors of one SPM5 "completely shot" although the fault he was chasing lay elsewhere in the supply.[4]
  • A supply that will not start, or that fails while the system boots.[4][2]
  • Disk errors with correct readings on a multimeter: on the Professional IRIS supply that This Old SGI describes, an oscilloscope showed the 5 V rail swinging between 4.5 and 5.3 V, caused by a failed input capacitor.[5]
  • A burnt or shorted tantalum capacitor on the boards or I/O bulkhead.[2]

See also Capacitor Failure Symptoms.

Identifying the supply

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The SGI Power-One supplies are SPM5 modular units: an input module, a backplane board and plug-in output modules, one per rail, each with its own isolation, rectifiers and output capacitors.[4][6] The supply in jan-jaap's 4D/380 rack is type SPM5M3B1M6S125, whose 5 V output module, the M3, is rated 250 A.[7] The SPM5 in an SGI Crimson is a different configuration, with a 170 A 5 V module; its capacitor values are on SGI Crimson Capacitor Replacement Guide.[4] Read the type label on your own supply, and note the module codes, before ordering.

Values reported by owners

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SPM5 M3 module (5 V, 250 A) from jan-jaap's 4D/380 rack
Group Original part Size (H × D), pitch Qty jan-jaap's replacement
1 United Chemi-Con SXF, 3900 µF 10 V, low impedance (21 mΩ, 2390 mA ripple) 40 × 12.5 mm, 5 mm 9 Panasonic FR 4700 µF 16 V, 35 × 12.5 mm (EEUFR1C472L)
2 United Chemi-Con SXC, 1000 µF 10 V, low impedance 22 × 12.5 mm, 5 mm 3 Panasonic FR 1000 µF 16 V, 16 × 10 mm (EEUFR1C102)
3 United Chemi-Con KMC, 47 µF 35 V, general purpose 105 °C 12 × 8 mm, 4 mm 3 Panasonic FR 47 µF 50 V, 2.5 mm pitch (EEUFR1H470)
4 United Chemi-Con SXJ, 470 µF 10 V, low impedance 15 × 8 mm, 5 mm 1 Panasonic FR 470 µF 10 V, 11.5 × 8 mm (EEUFR1A471)

[7]

jan-jaap's forum post describes the main bank as "a dozen" 3900 µF 10 V capacitors, where his chart lists nine; count the parts on your own module.[6][7] He chose larger values only for the output filter capacitors, for example 4700 µF 16 V in place of 3900 µF 10 V for the main bank, reasoning that one step up in capacitance and voltage gives about the original size with lower ESR and higher ripple-current capability, and kept every other part to its original value.[6][7] He used mostly Panasonic FR, a long-life 105 °C series with very low ESR and high ripple current.[4]

No owner has published capacitor values for the other modules of the 4D/380 supply, for the 4D/440 supply, or for LH Research, Cherokee or ACDC supplies in Power Series machines. For the Professional IRIS, This Old SGI records a failed capacitor in a pair of 2900 µF 200 V input capacitors on an LH Research MMA44-E192B, and says some twin-tower Power Series revisions may use the same supply.[5][8]

Recording your own supply

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Photograph each module before removing anything. For every electrolytic capacitor, note the module, designator, capacitance, voltage, series, temperature rating, diameter, height and lead pitch. jan-jaap's chart also records each part's ESR, ripple current and rated life, which helps when choosing replacements.[7]

Procedure

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The SPM5 rebuild follows the same steps as the Crimson supply, set out on SGI Crimson Capacitor Replacement Guide#Replacement procedure for a Power-One supply. Points from jan-jaap's Power Series rebuilds:

  1. Take the output modules out of the supply; each can be worked on alone.[4]
  2. Clean all electrolyte from the boards before soldering; new solder will not flow on a contaminated board. Where pads have lost their tin and corroded, robespierre recommends a fibreglass pen to get back to bright copper, then activated rosin flux and tinning with a cool iron, about 300 °C.[4]
  3. Check the bias supply MOSFET (a BUK456 in jan-jaap's supplies), which he found failed in most SPM5 supplies he has opened. He considered fitting it with a small TO-220 heat sink.[4]
  4. Check the fuse with a meter. The blown fuse in one of jan-jaap's supplies looked intact.[4]
  5. Re-secure loose components with a non-corrosive silicone. Forum members recommended DOWSIL 738; robespierre warns against acetoxy-cure silicone.[4]
  6. Before refitting the supply, test it on a load; jan-jaap uses an electronic load and a bank of power resistors.[2][6]

Boards

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On the first power-up of jan-jaap's 4D/380 after several years, with the backplane fitted but no boards, a tantalum capacitor near the keyboard port on the I/O bulkhead burst into flames. He concluded that all of them needed replacing, in the 4D/380, the 4D/440 and the Crimson, and replaced the electrolytic capacitors on the CPU and I/O boards before trying to boot them.[2] No values for these board capacitors have been published. Record each part's position, value, voltage and type as you go.

After the work

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  • Bench-test the supply under load before connecting it to the backplane, then power the backplane with no boards.[2]
  • Boot a minimal system: one I/O board, one CPU board, one MC2 and a serial console.[2]
  • See SGI Power Series Troubleshooting Guide for the status indicators.
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References

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  1. ↑ A. J. Corda, This Old SGI, version 2.0, July 1997, mirrored at sgistuff.net/mirrors/4dfaq.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 2.6 jan-jaap, "DALI, my PowerSeries 4D/380 VGX", IRIX Network forums, 27 June 2025, forums.irixnet.org. Supply rebuilds of the 4D/380, 4D/440 and Crimson; test load; tantalum failure; board recaps; minimal boot.
  3. ↑ Corda, This Old SGI, "Power Supply problems" (Power Series section). Supply makers and ratings.
  4. ↑ 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 jan-jaap, robespierre and others, "Rebuilding a PowerOne PSU for a 4D PowerSeries/Crimson", IRIX Network forums, April to May 2022, forums.irixnet.org. Isolation and residual charge, modules, cleaning, pad repair, bias MOSFET, fuse, silicone, Panasonic FR.
  5. ↑ 5.0 5.1 Corda, This Old SGI, "Professional Series Power Supply Problems". LH Research MMA44-E192B, 2900 µF 200 V input capacitors, rail noise.
  6. ↑ 6.0 6.1 6.2 6.3 jan-jaap, post of 14 June 2022 in "Tezro PSU rebuild process", IRIX Network forums, forums.irixnet.org. Power Series supply rebuilds; module design; capacitor upgrades; load before regulation.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 jan-jaap, capacitor replacement chart for the M3 module of the SPM5M3B1M6S125 supply in his 4D/380 rack, jurassic.nl/external/20220614-spm5/caps.png, posted 14 June 2022 (retrieved 22 October 2026).
  8. ↑ Corda, This Old SGI, "Hardware Troubleshooting" (Power Series section). Twin-tower supplies.


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