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SGI Visual Workstation 550 Capacitor Replacement Guide

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SGI Visual Workstation 550 M29A system board layout (User's Guide Figure 3-1)
M29A system board layout: power connector CN5 and the processor slots CPU1 and CPU2 at the left (User's Guide Figure 3-1)

No capacitor values have been published for the SGI Visual Workstation 550. SGI's user guide describes the M29A system board down to its connectors, jumpers and main chips, and treats the power supply as a sealed unit; it has no schematic or parts list.[1][2] No published photograph of a 550's system board or power supply shows readable capacitor markings.

Where the power circuitry is

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Power assemblies in the 550
Assembly What SGI documents
Power supply 450 W, switching between 110 V and 220 V by itself.[3] Above the system board at the rear, held by three screws, with leads to the system board and every drive. SGI warns that it can hold dangerous voltages even when unplugged.[2]
System board The M29A takes power at CN5, listed as the power connector, and has a second connector, CN3, that SGI's table calls "power assist".[1] SGI's layout drawing shows round capacitors and toroidal inductors around CN5 and beside the two processor slots.[1]
Battery BT1, a lithium cell for the clock and Setup memory; not a capacitor, but see SGI Visual Workstation 550 General Maintenance for replacement.[1]

The guide gives no DC output ratings for the supply; its physical specifications refer to the label on the back of the machine for power requirements.[4]

The Cobalt-based SGI Visual Workstation 540 uses a different supply, labelled for 587 W, and plug-in regulator cards; see SGI Visual Workstation 540 Capacitor Replacement Guide.

Symptoms that point at capacitors

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SGI's error table has no entry that names a capacitor. A machine that does not start at all, or that starts and then fails at random, should first be checked against SGI Visual Workstation 550 Troubleshooting Guide, which covers the AGP card, the RIMM pairing rules and the BIOS messages. For the signs of failed electrolytics in general (domed tops, electrolyte on the board, brown staining, a supply that will not start or cycles) see Capacitor Failure Symptoms.

Recording your own board's capacitors

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Without a parts list, the board in front of you is the only reference. Before removing anything:

  1. Take the system board out as described in SGI Visual Workstation 550 General Maintenance, and photograph both sides square on and in good light, so that the printing on the capacitor sleeves can be read. Do the same for the power supply board if you open it.
  2. For every electrolytic, note the designator printed on the board beside it, the capacitance, the voltage rating, the temperature rating, the maker and series, the can diameter and height, and the polarity stripe.
  3. List any solid polymer capacitors separately from the wet aluminium electrolytics.
  4. Replace like for like: the same capacitance, the same or a higher voltage rating, at least the same temperature rating and a low-ESR series wherever the original is in a regulator or supply output, with a can that fits the space.
  5. Keep the list and photographs with the machine for the next repair.

Safety

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The power supply runs from the mains, and SGI warns that it can hold dangerous voltages even when unplugged.[2] Unplug the machine, remove the supply, and discharge and measure the primary capacitors before touching anything on its board. See Recommended Tools for discharge tools and meters.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 Silicon Graphics, Inc., Silicon Graphics 550 Visual Workstation User's Guide, 007-4279-001, June 2000, chapter 3, "System Board", pp. 67–75: M29A board overview, Figure 3-1 (layout drawing, p. 72) and Table 3-1 (CN3 "Power assist", CN5 "Power connector", BT1 battery). Hosted as File:SGI Visual Workstation 550 User's Guide (007-4279-001).pdf.
  2. ↑ 2.0 2.1 2.2 Silicon Graphics 550 Visual Workstation User's Guide (007-4279-001), "Replacing the Power Supply", pp. 36–37.
  3. ↑ Silicon Graphics, Inc., Release Notes for the Silicon Graphics 550 Visual Workstation, 007-3941-002, 2001, item 6. Hosted as File:SGI Visual Workstation 550 Release Notes (007-3941-002).pdf.
  4. ↑ Silicon Graphics 550 Visual Workstation User's Guide (007-4279-001), Appendix B, Table B-1, p. 137.


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