SGI Onyx Capacitor Replacement Guide
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The SGI Onyx has electrolytic capacitors in its offline switcher (OLS), on its power boards and around the DC-DC converters on its system boards. SGI's documents treat every board, power board and the OLS as a replaceable unit and give no component values for any of them, and no owner has published a capacitor list for the Onyx or for the CHALLENGE, which uses the same power system.[1][2] Read the values from your own boards; never fit a value taken from someone else's board without checking it against yours.
Warning: the OLS rectifies the mains, and its output is 48 V at up to 50 A. The 48 V stays on the backplane whenever the OLS is running, even with the system halted.[3][4] SGI's 2000 hazard letter tells owners to let an OLS cool for 30 minutes after shutdown before removing it.[5]
Where the power conversion is
[edit | edit source]| Assembly | What is known |
|---|---|
| OLS (013-0513) | Made by Cherokee International in two power ratings; converts the mains to 48 V DC. SGI's documents give no schematic or parts list for it. |
| Power boards (303, 305, 512, 512T, 505, 505x2) | Built around sealed DC-DC converter modules; the 303 carries two AT&T FW300 3 V converters. |
| CPU boards (IP19, IP21, IP25) | A 5 V and a 3.3 V converter brick on each board; radial electrolytics beside them on the IP19. |
| MC3 memory board | One 5 V brick, with provision for a 3.3 V brick on later boards. |
| IO4 and VCAM | 1.5 V regulators on the IO4; 1.5 V, −5.2 V and −12 V regulators on the VCAM. |
| System Controller power board | Its own converters for V5_AUX and −14.5 V (LT1076HVCT switching regulators) and a 1.5 V brick. |
Electrolytic capacitors sit around these converters. The photograph above shows nine radial electrolytic capacitors around the two converter heat sinks on an IP19, with the silkscreen marking the 5 V and 3.3 V sides; their values cannot be read at this resolution.[7] jan-jaap's close-up photographs of a System Controller board on the IRIXNet forum show several large radial electrolytics and two toroidal inductors around its 1.5 V brick and LT1076HVCT regulators, with tantalum capacitors nearby; the values are only partly legible.[6] The RealityEngine2 GE10V board has two small radial electrolytics at its top edge in the photograph in SGI Onyx.
Which parts matter
[edit | edit source]- The OLS. The fault SGI documented in it is in the inductors: SGI found that after two to seven years the magnetic cores could run hot enough to make their insulation smoke and occasionally burn. SGI's remedy was a newly made OLS with better core material, so new capacitors in an old OLS do not remove that risk.[5] jan-jaap names the last revision of the InfiniteReality-capable OLS, 060-0120-001 Rev A (2400 W, 48 V at 50 A), as the only "safe" one.[8]
- The converter modules on the boards are sealed and cannot be serviced, and jan-jaap has never managed to desolder anything from the thick CPU, memory and I/O boards.[9] The electrolytics beside the modules are the parts an owner can reach.
- The VCAM's negative-voltage regulators fail more often than the positive converters in jan-jaap's experience, and the System Controller's own 5V_AUX regulator has failed on one of his boards.[10][6] Check the capacitors around both when chasing a POKA fault or wrong voltage readings.
- jan-jaap does not recommend replacing capacitors blind in SGI supplies; he keeps spare units and repairs what has actually failed.[9]
Recording your own board
[edit | edit source]- Photograph each board before removing anything, square on and at an angle, so the printing on every capacitor can be read later.
- For each electrolytic note the silkscreen position (the System Controller board in jan-jaap's photographs is marked with grid references such as H8C2 and G6B5), the capacitance, voltage, temperature rating, maker and series, diameter and height, and which way round it is fitted.[6]
- Measure ESR and capacitance out of circuit. A part that is leaking, bulging, high in ESR or low in capacitance needs replacing.
Replacing a capacitor
[edit | edit source]- Shut IRIX down, turn the key to Off, switch off the breaker and unplug the machine.[11] After any overheating, wait 30 minutes before touching the OLS.[5]
- Remove the board as described in SGI Onyx General Maintenance, using an earthed wrist strap.
- Fit a part of the same capacitance, the same or higher voltage, at least the original temperature rating and low ESR where the original sits beside a converter. Check the polarity marking on the board before soldering.
- Clean off any electrolyte and check the tracks under the old part.
Checks after the repair
[edit | edit source]Refit the board and power up with the key. The System Controller stops the start-up and reports a POKA or POKB fault if any converter group is out of range, and the board's red fault LED shows which converter.[2] With the key in Manager, the Voltage Status menu shows the 48 V from the OLS, the 512 board's 5 V and 12 V, the System Controller's 1.6 V termination supply and the VCAM's negative rails.[2][6] The OLS shuts itself down if its output goes below 45 V or above 50 V.[2] The test sockets on the boards take 2 mm plugs.[6] See SGI Onyx Troubleshooting Guide for the meaning of each message, and Capacitor Failure Symptoms for what a failed capacitor looks like.
Related pages
[edit | edit source]- SGI Onyx
- SGI Onyx General Maintenance
- SGI Onyx Troubleshooting Guide
- Capacitor Failure Symptoms
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 Silicon Graphics, CHALLENGE and Onyx Rack and Deskside Illustrated Parts List, 108-0129-002, 1995, chapters 3 and 4 (File:SGI CHALLENGE and Onyx Rack and Deskside Illustrated Parts List (108-0129-002).pdf). Board-level part numbers only, including the OLS assembly 013-0513; no component lists.
- ↑ 2.0 2.1 2.2 2.3 2.4 Silicon Graphics, CHALLENGE/Onyx Diagnostic Road Map, 108-7045-030, 1994, chapter 3, pp. 3-1 to 3-16 (File:SGI CHALLENGE and Onyx Diagnostic Road Map (108-7045-030).pdf). Power boards and bricks, regulator locations, fault LEDs, Voltage Status menu, OLS output limits.
- ↑ 3.0 3.1 Mark, "SiliconGraphics Onyx Teardown", iFixit, January 2013, steps 16–17, ifixit.com. 303 board with two AT&T FW300 converters; OLS 48 V, 50 A, 2400 W.
- ↑ Silicon Graphics, POWER Onyx and Onyx Rackmount Owner's Guide, 007-1736-060, 1996, p. 45 (File:SGI POWER Onyx and Onyx Rackmount Owner's Guide (007-1736-060).pdf). 48 V present on the midplane when halted.
- ↑ 5.0 5.1 5.2 5.3 SGI, Potential Hazard Regarding Off-Line Switching (OLS) Power Supply, customer letter 007-4267-001, 21 August 2000 (File:SGI Challenge and Onyx OLS power supply hazard letter (007-4267-001).pdf). Cherokee International OLS in two ratings, inductor core overheating, replacement supply, 30-minute cooling time.
- ↑ 6.0 6.1 6.2 6.3 6.4 6.5 jan-jaap, "Challenge/Onyx Power Subsystem troubleshooting", IRIXNet forum, 7–13 December 2021, forums.irixnet.org. System Controller photographs, LT1076HVCT regulators, 1.5 V brick, voltage display, 2 mm test sockets.
- ↑ Retro-Computing Society of Rhode Island, photograph of an SGI IP19 CPU board, 28 October 2009, CC BY-SA 3.0 (File:SGI IP19 CPU board (RCS-RI).jpg).
- ↑ jan-jaap, reply of 22 March 2019 in "SGI Onyx restoration", IRIXNet forum, forums.irixnet.org. OLS revisions.
- ↑ 9.0 9.1 jan-jaap, reply of 17 January 2019 in "Proactive maintainability of SGI Power Supplies, thoughts?", IRIXNet forum, forums.irixnet.org. Sealed converter modules, thick boards, his view on blind capacitor replacement.
- ↑ jan-jaap, replies of 13 September 2021 in "SGI Challenge L 12VDC Undervoltage", IRIXNet forum, forums.irixnet.org. VCAM inverting regulators.
- ↑ Silicon Graphics, POWER Onyx and Onyx Deskside Owner's Guide, 007-1733-070, 1996, p. 78 (File:SGI POWER Onyx and Onyx Deskside Owner's Guide (007-1733-070).pdf). Powering off.
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