SGI Power Indigo² Capacitor Replacement Guide

Component side of the R8000 CPU module. SGI says the capacitors that help control its clocks are on the back of the module (SGI, 108-0130-001 Figure 1-2)

Silicon Graphics published no capacitor list or values for the SGI Power Indigo²: not for its power supply, its IP26 system board or its R8000 CPU module. Its documents for the R8000 machines treat the supply, the system board and the module as replaceable parts. The supply is the Indigo² supply, revision S or later, so the recapping method on SGI Indigo² Capacitor Replacement Guide applies to it. What follows covers the points that differ on the R8000 machine, the one value owners have reported, and how to record your own board.

Warning: the power supply runs from the mains. Unplug it, let the input capacitors discharge and check them with a meter before touching the boards.

Where the capacitors are

Power supply

weblacky says SGI did not design its own power supplies, and that the supplies in every SGI he has seen are other makers' designs carrying a large number of electrolytic capacitors, which makes them the usual first point of failure. The supply in one owner's POWER Indigo² is a non-IMPACT type: he describes a case in which the left side, top and bottom are one piece with the fan end, leaving only the right-hand panel and the back plate, which carries the board that links the upper and lower boards, as separate parts. The SGI Indigo² capacitor guide covers opening that type.

System board and audio board

weblacky also notes that the Indigo² has electrolytic capacitors in its GIO-64 backplane module and here and there on the system board, where the Indy board uses tantalum capacitors, though few failures had been reported when he wrote in 2024. SGI describes the IP26 layout as largely that of the IP22. One owner found a report of the audio board capacitor C57 failing on an R8000 Indigo²; the audio board is the one an R8000 upgrade moved across from the old IP22 board. See the table below.

R8000 CPU module

SGI says several capacitors on the back of the R8000 module help control its internal clocks, and that if any one of them is damaged the module will not work. Its warnings are about knocking and scraping them: do not set the module down roughly on a hard surface, do not scrape its underside on the chassis, and keep it clear of the 3.5-inch drive bay while fitting it. SGI gives no type or value for these capacitors and no instruction to replace them, and says not to use an ohmmeter on the module.

Values reported by owners

Capacitors reported on Indigo² machines including the POWER Indigo²

Assembly	Position	Original	Notes
Audio board	C57	47 µF 20 V tantalum	Shorted on an R4400 Indigo², burning out inductor L517 and a pad. The owner found a report of the same capacitor failing on an R8000 Indigo².

The owner replaced C57 with a 100 µF 16 V Rubycon ZLH electrolytic because it was the smallest suitable part he had, and said a part of the same capacitance and voltage would be better. No owner has published the capacitor values of a POWER Indigo² power supply. The values on the SGI Indigo² Capacitor Replacement Guide are from a later IMPACT supply, which is a different unit.

Recording your own board

Photograph each board before removing anything. For every electrolytic capacitor, note the designator, capacitance, voltage, temperature rating, series, diameter, height and lead spacing, and mark the polarity on your photograph. Note the revision letter on the side of the supply as well.

Procedure

1. Take the R8000 module out if it covers the supply connector, then remove the supply; see SGI Power Indigo² General Maintenance#R8000 CPU module and SGI Power Indigo² General Maintenance#Power supply.
2. Recap the supply following SGI Indigo² Capacitor Replacement Guide#Procedure. weblacky's advice is to replace every electrolytic capacitor, including the expensive ones; to choose parts close to the originals in ESR, ripple rating, life and temperature rating as well as value, because modern low-ESR types can upset the supply's oscillation; and to check the MOSFETs, then the resistors and low-voltage diodes, out of circuit.
3. Check the audio board's tantalum capacitors, C57 in particular, with the board out of the machine.
4. Inspect the back of the R8000 module by eye for cracked or missing parts. If one is damaged, record its markings and size before looking for a replacement, since SGI gives no values.

Checks after the work

• Test the supply in the machine, not on the bench. weblacky says an Indigo² supply does not regulate without a load, so a bench run shows only that it starts.
• SGI gives the nominal output of the 3.3 V rail on revision S and later supplies as 3.45 V, which the R8000 needs.
• At the Command Monitor, hinv -v should report the IP26 system, the 75 MHz R8000 and the 2 MB secondary cache.
• Leave the machine running for at least an hour. Indigo² supplies have been reported tripping after 30 to 60 minutes; see SGI Indigo² Troubleshooting Guide.

Related pages

• SGI Power Indigo²
• SGI Power Indigo² General Maintenance
• SGI Power Indigo² Troubleshooting Guide
• SGI Indigo² Capacitor Replacement Guide
• Capacitor Failure Symptoms
• Recommended Tools