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SGI Visual Workstation 320 Capacitor Replacement Guide

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SGI Visual Workstation 320 system board power area (bronchitis, IRIXNet 2020)
Power area of a Silicon Graphics 320 system board: Nichicon electrolytics around the CS5155 controller, beside the main and auxiliary power connectors (bronchitis, IRIXNet forum, 2020)

SGI's Owner's Guide for the SGI Visual Workstation 320 treats the power supply and the system board as parts to be replaced whole and gives no component values, and no schematic or parts list for either has been published.[1][2] What is known is where the electrolytic capacitors are and what one photographed board carries. Take every value from the part on your own board.

Where the electrolytic capacitors are

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  • The power supply is SGI's own unit, rated at 485 W input, with a voltage selector switch, soft power control and a power good output.[3] Its internal construction is not documented.
  • On the system board, a photograph of a 320 board posted to the IRIXNet forum in May 2020 shows about ten brown-sleeved Nichicon electrolytic capacitors grouped between the main power connector, the auxiliary connector and the front-panel power header. They surround a CS5155 controller, with a MAX495 beside it, and the board's printed designators in that area include C123, C189, C211, C215 and C217. Their values cannot be read in the photograph.[4]
  • The plug-in voltage regulator for the second processor is a separate module, sold under VXI part numbers, that fits in the socket above the processors.[5][6]

The SGI320 community site identifies U37 on the 320 system board as a Cherry CS5155 buck controller, the controller of the on-board processor voltage regulator, and describes a modification SGI made to it on many revision 006 boards.[7] The capacitors around the CS5155 in the photograph are therefore on a switching regulator. Read the series printed on each sleeve before choosing a replacement, and keep to a low-ESR series where the original is one.

Signs of failure

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The IRIXNet forum's capacitor threads concern other SGI models, not the 320, and the SGI320 site describes no capacitor failure. In the one forum thread about a 320 that would not start, the owner reported that the board's capacitors looked fine, and the thread ended without a cause.[4] Look for domed tops, electrolyte on the board, and sleeves that have shrunk or split, and see Capacitor Failure Symptoms.

Recording your board

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Before ordering parts, make your own list:

  1. Remove the power supply to get a clear view of the board; Digital Content Creators noted in 1999 that the supply has to come out for full access to the system board.[8][2]
  2. Photograph the board in sections, square-on, with enough light to read the sleeves.
  3. For each electrolytic, write down the printed designator, the capacitance, the voltage rating, the temperature rating, the series name and the can diameter and height.
  4. Note which rail each one sits on: with the board powered, measure the voltage at its positive lead against chassis ground, or trace it to the main connector pins (+3.3 V, +5 V, +12 V) given in SGI Visual Workstation 320 Troubleshooting Guide.
  5. Record the board revision printed on the board; the SGI320 site lists several revisions of the 320 board, and parts may differ between them.[9]

Replacement

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  1. Unplug the workstation, remove the side cover, the power supply and any PCI cards, and take out the DIMMs and processors that are in the way.[2][10][5]
  2. Take the system board out of the chassis. Keep its screws together; the SGI320 site reports loose board screws causing power-up faults.[11]
  3. Fit replacements of the same capacitance and at least the same voltage rating, in a low-ESR series where the original is one, and no taller or wider than the original: the capacitors sit close to the DIMMs and processors.
  4. Observe polarity. The stripe on the sleeve marks the negative lead.
  5. Refit the board and supply and check that both power supply cables, and the power button and LED cables, are seated before the first power-up.[1]
  6. Run the firmware's Extensive Tests once after the work.[12]

Warning: the power supply carries mains voltage, and its input capacitors can hold a dangerous charge after it is unplugged. Leave it unplugged until they have discharged, and confirm with a meter before touching the primary side.

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References

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  1. ↑ 1.0 1.1 SGI, 007-3701-001, pp. 89-93, Table 8-1. Power supply and system board as replaceable units; cable checks.
  2. ↑ 2.0 2.1 2.2 SGI, 007-3701-001, pp. 79-83. Removing the power supply as a unit.
  3. ↑ Silicon Graphics, Inc., Silicon Graphics 320 Visual Workstation datasheet, 1999 (File:SGI 320 Visual Workstation Datasheet (1999).pdf). 485 W input supply, switch-selected input, soft power, power good.
  4. ↑ 4.0 4.1 "SGI Visual Workstation 320 won't POST", IRIXNet forum, thread started by bronchitis, April to May 2020, with photographs of the board posted on 4 and 6 May 2020, forums.irixnet.org. Forum search for "capacitor" checked 21 October 2026.
  5. ↑ 5.0 5.1 SGI, 007-3701-001, pp. 65-77. Processor removal and the voltage regulator for the upper slot.
  6. ↑ Milton Adamou, "VRM", SGI320, sgi320.wordpress.com. VXI regulator module part numbers.
  7. ↑ Bob Skiles, "U37 Hack", SGI320 community site, sgi320.wordpress.com. U37 is a Cherry CS5155 buck controller in the on-board regulator.
  8. ↑ J. V. Bolkan, "SGI 320 NT Workstation Includes Striking Differences", Digital Content Creators Magazine, 6 August 1999, dccmag.com. The supply must be removed for full access to the system board.
  9. ↑ Milton Adamou, "CPU", SGI320, sgi320.wordpress.com. Known system board revisions.
  10. ↑ Silicon Graphics, Inc., Silicon Graphics 320 Visual Workstation Owner's Guide, 007-3701-001, 1999, pp. 23-28 (File:SGI Visual Workstation 320 Owner's Guide (007-3701-001).pdf). Removing DIMMs.
  11. ↑ Milton Adamou, "Other" FAQ, SGI320, sgi320.wordpress.com. Loose system board screws causing power-up problems.
  12. ↑ Silicon Graphics, Inc., Silicon Graphics Visual Workstations System Firmware User's Guide, 007-4225-001, 1999, p. 8 (File:SGI Visual Workstations System Firmware User's Guide (007-4225-001).pdf). Extensive Tests.


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