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SGI IRIS 3000 Capacitor Replacement Guide

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SGI IRIS IP2 board capacitor legend (schematic 5000-556)
Capacitors and other discrete parts of the IP2 processor board, from the legend on sheet 1 of SGI's schematic 5000-556

SGI published no capacitor list for the SGI IRIS 3000 power supply. What is known about the machine's capacitors comes from SGI's board schematics on bitsavers and from bitsavers' photograph of an IP2 board.[1][2]

Warning: the power supply runs from the mains. Unplug the cabinet, let the input capacitors discharge and check them with a meter before touching the supply.

Power supply

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The cabinet has a 720 W supply with four outputs, +5 V (channel 1), +12 V (channel 2), −12 V (channel 3) and −5 V (channel 4), each with its own current-limit, over-voltage and voltage adjusters.[3][4] SGI's 68020 course lists the power supply among the field-replaceable units, and its lab work does not go beyond finding the supply's fixing screws.[5][6] The only lead Levine had on the supplies in 1993–94 was an old telephone number for LH Research, which was no longer in service.[7] No schematic, component list or capacitor values for the supply have been published.

Boards

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SGI's schematics for four of the boards list their bulk capacitors, all at the Multibus power pins:

Bulk capacitors on the IRIS 3000 boards (SGI schematics)
Board Parts Value Rail Type given
IP2 (processor) C1, C2 100 µF +5 V (VCC) Polarised; type not stated
IP2 C3 40 µF −5 V (VEE) Polarised; type not stated
IP2 C20 10 µF – Not stated
IM1 (memory) C1, C2 100 µF +5 V Tantalum
UC4 (update controller) C1, C2 40 µF +5 V Polarised; type not stated
BP3 (bitplane) 2 parts 40 µF +5 V Polarised; type not stated

[1][8][9][10] The schematics give no voltage ratings. In bitsavers' photograph of an IP2 board, the large parts at the Multibus edge are axial capacitors printed "KEMET T110", and the other capacitors visible on the board are small dipped parts.[2] No schematics of the GF2, DC4 or FP1 boards have been found; Levine was looking for them in 1993.[7]

Recording your own parts

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Before ordering anything, photograph each board and the supply, and write down for every capacitor its designator, value, voltage, type (aluminium electrolytic or tantalum), temperature rating, size and lead spacing. Look up each part's series from its markings before choosing a replacement, since the schematics only name tantalum parts on the IM1.[8]

Checks after any work

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SGI's settings for the supply, measured at its terminal block with a normal load, are +5.00 V on channel 1, +12.10 V on channel 2, −12.10 V on channel 3 and −5.24 V on channel 4.[11] Then run the stand-alone memory and floating-point tests from the diagnostic tape; see SGI IRIS 3000 Troubleshooting Guide#Stand-alone diagnostics.[12]

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References

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  1. ↑ 1.0 1.1 Silicon Graphics, IP2 PCB schematic, 5000-556 revision C, 14 November 1985, sheet 1, discrete legend and representative bypass capacitors (File:SGI IRIS IP2 processor board schematic (5000-556).pdf).
  2. ↑ 2.0 2.1 Bitsavers, photograph of an IP2 board (assembly 5000-561), bitsavers.org/pdf/sgi/iris/3130/boards/IP2/IP2.jpg (viewed 22 October 2026).
  3. ↑ Silicon Graphics, IRIS 3000 Series Workstation Differences (field-service study guide), lesson PROD10, pp. 6 to 8 (File:SGI IRIS Series 3000 Workstation Differences Course.pdf).
  4. ↑ SGI, IRIS 3000 Series Workstation Differences, lesson COMP1, Diagram 14, p. 22.
  5. ↑ Silicon Graphics, IRIS Workstation Course, 68020 Based, Student Workbook part 2, lesson 5 objectives (File:SGI IRIS Workstation Course 68020 Based Student Workbook Part 2.pdf).
  6. ↑ SGI, IRIS 3000 Series Workstation Differences, lesson COMP1, step 8, p. 7.
  7. ↑ 7.0 7.1 Jonathan Levine, "Silicon Graphics IRIS 2000/3000 FAQ", revisions of May 1993 to June 1994, sections 3.2 and 4.4.2, bitsavers.org/pdf/sgi/iris/IRIS_FAQ.txt.
  8. ↑ 8.0 8.1 Silicon Graphics, IM1 PCB schematic, 5000-529 revision A, 10 June 1985, sheet 1, discrete legend (File:SGI IRIS IM1 memory board schematic (5000-529).pdf).
  9. ↑ Silicon Graphics, UC4 update controller schematic, 5000-508 revision A, 6 March 1985, sheet 1, discrete component legend (File:SGI IRIS UC4 update controller schematic (5000-508).pdf).
  10. ↑ Silicon Graphics, BP3 PCB schematic, 5000-500 revision B, 30 April 1986, sheet 1 (File:SGI IRIS BP3 bitplane board schematic (5000-500).pdf).
  11. ↑ SGI, Student Workbook part 2, lab 8.1, section 5 "Power Supply Adjustments", p. 31.
  12. ↑ SGI, IRIS 3000 Series Workstation Differences, lesson DIAG10, pp. 8 to 14.


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