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SGI Onyx2 Capacitor Replacement Guide

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SGI Onyx2 deskside midplane and boards (Owner's Guide Figure 2-2)
Onyx2 deskside midplane with the Node, graphics, BaseIO and XIO boards drawn out (SGI Deskside Owner's Guide, Figure 2-2)

The SGI Onyx2 has electrolytic capacitors in its module power supply, on the midplane near the power connectors and on its boards. SGI's owner's guides treat the supply and the boards as units for its own engineers and give no component values, and no owner has published a capacitor list for any of them.[1][2] The deskside and compute modules use the same family of supply as the SGI Origin 2000, and the one documented repair of that supply, with its disassembly, is on SGI Origin 2000 Capacitor Replacement Guide. Read the values from your own boards; never fit a value taken from someone else's board without checking it against yours.

Warning: the supply runs from 110 V or 200–240 V mains, and its input capacitors can hold a charge after the cord is pulled. Switch off the rear breaker, unplug the cord and confirm with a meter that the input capacitors are discharged before working inside. Turning the MSC key to Standby does not remove power from the midplane.[3]

The module power supply

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SGI's deskside guide describes the supply as autoranging, with outputs of +12 V, +5 V and +3.45 V, and three LEDs on its front: amber for AC present, green for outputs within specification and red for a fault shutdown.[3][4][1] Owners on the IRIXNet forum treat the Onyx2 and Origin 2000 supplies as one family.[2][5]

Pentium's Origin 2000 supply failed in 2024 because leaking Nichicon capacitors near the primary MOSFETs had eaten through a gate-drive trace. He counted over 70 capacitors in the supply and concluded that it needs a complete recapacitoring, down to the control boards.[2] jan-jaap notes that the wires between its circuit boards are soldered, so it does not come apart easily.[6] For the disassembly steps and the record sheet, see SGI Origin 2000 Capacitor Replacement Guide.

Rack graphics module supplies

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Each graphics module in an Onyx2 rack has its own supply and breaker, separate from the compute module's.[7] Two failures have been reported on the IRIXNet forum. bjornl's supply popped and gave off a smell when switched on, and a piece of white ceramic fell out of it, which Irinikus took to be part of a ceramic power resistor.[5] jdanna replaced what looked like a blown capacitor in another, and it then failed more violently; coldbug suggested a tantalum capacitor as the first thing to check. Raion describes these supplies as uncommon compared with the standard Onyx2 and Origin 2000 supplies.[5]

Midplane

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kaigan describes a large group of big electrolytic capacitors on the deskside midplane beside its two white power connectors.[8] CB_HK found an exploded tantalum capacitor on his midplane, and jan-jaap read the value of the same position on a spare midplane as 33 µF 25 V.[6] Several positions on the midplane are deliberately unpopulated, so compare with a known-good midplane before deciding that a part is missing.[8]

Recording your own board

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  1. Photograph each board before removing anything, so the printing on every capacitor can be read later.
  2. For each electrolytic note the board, position, capacitance, voltage, temperature rating, maker and series, diameter and height, and which way round it is fitted.
  3. Measure ESR and capacitance out of circuit; a part that is leaking, bulging, high in ESR or low in capacitance needs replacing.
  4. Fit a part of the same capacitance and at least the same voltage and temperature rating, check the polarity on the board, and clean away any electrolyte. Inspect the tracks near a leaking part under magnification: the damage in Pentium's supply was visible only under a microscope.[2]

Checks after the repair

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  1. With the breaker on, the amber LED on the supply and the AC OK LED on the MSC should light.[4][1]
  2. Turn the key to On. DC OK should light about 3.5 seconds later, the supply's green LED should stay on and the MSC should show SYS OK.[4]
  3. A blinking red LED means undervoltage on +3.45 V, +5 V or +12 V; a blinking green LED means overload.[1]
  4. The MSC can move the 3.45 V and 5 V outputs 5% up or down from its diagnostic port for margin testing.[4]

See SGI Onyx2 Troubleshooting Guide for the MSC messages and Capacitor Failure Symptoms for what failed capacitors look like.

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References

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  1. ↑ 1.0 1.1 1.2 1.3 SGI, 007-3454-005, chapter 7, pp. 97–98. Supply not end-user replaceable; supply LEDs.
  2. ↑ 2.0 2.1 2.2 2.3 Pentium, "Onyx2/Origin 2000 Power Supplies and Capacitors - It's time, folks", IRIXNet forum, 27 December 2024, forums.irixnet.org.
  3. ↑ 3.0 3.1 Silicon Graphics, Silicon Graphics Onyx2 Deskside Workstation Owner's Guide, 007-3454-005, 1999, chapter 3, pp. 32 and 42 (File:SGI Onyx2 Deskside Workstation Owner's Guide (007-3454-005).pdf). Autoranging supply; key switch does not remove midplane power.
  4. ↑ 4.0 4.1 4.2 4.3 SGI, 007-3454-005, chapter 6, pp. 90–92. MSC LEDs, DC OK voltages, margining.
  5. ↑ 5.0 5.1 5.2 bjornl and Irinikus, "Repair Onyx2 graphics module power supply", IRIXNet forum, 7 October 2018, forums.irixnet.org; jdanna, Raion and coldbug, "WANTED: Onyx2 rack graphics power supply", 14 July 2021, forums.irixnet.org.
  6. ↑ 6.0 6.1 jan-jaap and CB_HK, "Onyx2 Restoration (WIP)", IRIXNet forum, 19 March 2019, forums.irixnet.org.
  7. ↑ Silicon Graphics, Silicon Graphics Onyx2 Rackmount Owner's Guide, 007-3457-005, 2000, chapter 4, pp. 95–99 (File:SGI Onyx2 Rackmount Owner's Guide (007-3457-005).pdf). Graphics module breakers and power cables.
  8. ↑ 8.0 8.1 kaigan and jan-jaap, "Onyx2 Deskside Midplane Capacitor/Resistor Identification", IRIXNet forum, 31 August to 4 September 2019, forums.irixnet.org.


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