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SGI IRIS 1000 Capacitor Replacement Guide

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SGI IRIS system in a Silicon Graphics advertisement (Computer Design, April 1984)
An IRIS system of 1984 (Silicon Graphics advertisement, Computer Design, April 1984)

Almost nothing has been published about the capacitors in the SGI IRIS 1000 series. No SGI schematic or parts list has been found for the PM1 or PM2 processor boards, the GF1, UC3, DC3 and BP2 graphics boards or the power supply, and Levine's IRIS FAQ, written for the later 2000 and 3000 series, covers the 1000 series only in outline.[1] No capacitor values for these machines have been published.

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.

What is known

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  • In bitsavers' photograph of a PM2 board (the processor of the 1400 and 1500), the capacitors visible are small dipped parts; no large can capacitors are visible on that board.[2][3]
  • The only SGI note on the 1000 series' power arrangements concerns the backplane, not capacitors: machines shipped before February 1984 lack the voltage-limiting diode assembly that provides 4.1 to 4.3 V for GF1 boards with 4 V Geometry Engines, which SGI added by a field change order.[4]
  • The 2000 and 3000 series that followed have SGI board schematics listing their bulk capacitors; those are on SGI IRIS 3000 Capacitor Replacement Guide, but they apply to different boards.[3]

Recording your own parts

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Before replacing anything, photograph each board and the power supply, and write down, for every capacitor, its designator, value, voltage, type (aluminium electrolytic or tantalum), temperature rating, size and lead spacing. Identify each part's series from its markings, and keep the record so that later owners have something to compare with. If you work on the power supply, measure its outputs under load before and after and keep those readings too.

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References

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  1. ↑ Jonathan Levine, "Silicon Graphics IRIS 2000/3000 FAQ", revisions of May 1993 to June 1994, sections 2.1, 3.2 and 4.4.2, bitsavers.org/pdf/sgi/iris/IRIS_FAQ.txt.
  2. ↑ Bitsavers, photograph of a PM2 board (assembly 5000-065) filed with the IRIS 1400 material, bitsavers.org/pdf/sgi/iris/1400/PM2.JPG (viewed 22 October 2026).
  3. ↑ 3.0 3.1 R. Stricklin, "WTB: SGI (MIPS architecture) Systems", rescue mailing list, 26 May 2010, bitsavers.org/pdf/sgi/iris/bear_sgi_may2010.txt.
  4. ↑ SGI Field Engineering, Technical Aid GEN-010, "Backplane Voltage Limiter for GF1 Board", IRIS 1000 and 1200, 13 February 1984, in IRIS Workstation Course, 68020 Based, Student Workbook part 2 (File:SGI IRIS Workstation Course 68020 Based Student Workbook Part 2.pdf).


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