SGI Personal Iris Capacitor Replacement Guide

Bottom: an original L&H Research Personal IRIS supply on its bracket, with its large input electrolytics. Top: a Power-One PFC375-4000 fitted to the same bracket as a replacement (photo: jan-jaap)

Capacitor notes for the SGI Personal Iris. Two parts of the machine are covered here: the L&H Research power supply, for which no component list has been published, and the IP10 CPU board of the 4D/25, whose capacitors SGI's own bill of materials lists. jan-jaap, a collector on the IRIX Network forum, says the Personal IRIS has a reputation for its supplies dying and suggests replacing their electrolytic capacitors before they fail.

Warning: the supply runs from mains and its input capacitors hold a dangerous charge after the cord is pulled. Unplug the machine, let the supply stand, and confirm with a meter that the input capacitors have discharged before touching anything inside it. The supply board is mounted on a bracket that also serves as its heat sink, so it cannot be run safely with the solder side exposed for probing.

The power supply

The original supply is an L&H Research CM-E2348A (SGI part 9430801, L&H P/N 853874-002), rated 350 W from 115 or 230 V: +5 V at 45 A, +12 V at 9 A and −12 V at 2 A. It has two replaceable fuses, one on its small daughtercard and one beside it under a blue plastic cap. The two-wire green and brown cable from it powers the supply fan.

No value list for its capacitors has been published, so record them from the board as you work. Owners report two kinds of failure:

• Mains suppression capacitors. One owner found a blown suppression capacitor in his supply and read it as 0.6 µF, 250 V, and jan-jaap agreed with his reading. jan-jaap advises replacing all of these capacitors even if they look sound, because they absorb moisture with age, crack and then blow; he says Kemet still makes them. robespierre, another forum member, explains that they are metallised paper types rated X2 for use across the mains, that they only suppress interference, and that polypropylene film types of the same size and rating can replace them.
• Complete failure with no outputs. jan-jaap's supply hummed faintly with none of its outputs present; he chose a new replacement supply over a repair because the bracket makes live fault-finding so awkward.

The IP10 CPU board (4D/25)

SGI's bill of materials for the IP10 assembly (300-8029-001, effective 20 June 1989) lists these polarised capacitors, all triple-lead tantalum types:

IP10 tantalum capacitors (SGI bill of materials 300-8029-001)

Value	Rating	SGI part	Quantity	Locations
220 µF	10 V	9050823	5	03I4, A5K2, A5B7, 02A2, B5A5
33 µF	16 V	9050824	2	03J5, 03J7
2.2 µF	16 V	9050822	2	J1B7, J3B7
1 µF	printed "20DC"	9050821	3	F6A5, E8A5, F2A5

The schematic's sheet 30 shows where the larger ones sit on the power input: 03I4, A5K2, A5B7 and 02A2 across +5 V at the J6 power connector, 03J7 across +12 V and 03J5 across −12 V. When jan-jaap first powered a spare IP10 board from a new supply, a tantalum capacitor on its 12 V rail exploded; the board still worked once the remains had been removed. If you replace 03J7 or 03J5, keep at least the 16 V rating and observe polarity: 03J5 is fitted with its positive end to ground.

IP10 power input: J6 with the 220 µF capacitors on +5 V and the 33 µF capacitors on +12 V and −12 V (SGI schematic 032-8029-001, sheet 30)

SGI's IP6 schematic for the 4D/20, hosted here, has no bill of materials, and none of SGI's documentation for the IP14 and IP12 boards of the 4D/30 and 4D/35 is hosted.

Recording your own supply

1. Unplug the machine, remove the E-module and take out the supply on its bracket (see SGI Personal Iris General Maintenance).
2. Photograph both sides of the board before desoldering anything, with designators readable.
3. For each electrolytic, write down the designator, capacitance, voltage rating, temperature rating, maker and series, can diameter and height, lead spacing and polarity. For the suppression capacitors, note the capacitance, voltage and safety class (X2 or Y2).
4. Look for domed tops, leakage, brown or crystalline residue, cracked suppression capacitor bodies, and corroded traces.
5. Measure ESR with the part out of circuit and compare it with the maker's figure for that series.

Record sheet

Position	Designator	Capacitance	Voltage	Temperature or class	Series	Size	Condition
Supply, mains input and suppression
Supply, primary
Supply, secondary

Replacing

• Electrolytics: fit the same capacitance and at least the same voltage rating, 105 °C parts, and low-ESR series wherever the original was a low-ESR type.
• Suppression capacitors: use parts of the same safety class (X2 across the line), capacitance and voltage rating, in the same size.
• Tantalums on the CPU board: same capacitance, at least the same voltage rating, correct polarity.
• Observe polarity throughout; mark it on your photographs before removal.

After the repair

1. Refit the supply and its fan cable, and reconnect the power switch wires.
2. Before refitting the E-module, measure the outputs at the supply connectors: +5 V, +12 V and −12 V.
3. With a replacement supply, check the readings under load. An owner fitting a Power-One unit saw 10.8 V on the 12 V output with no load; robespierre explained that this is what a group-regulated supply that takes its feedback from the 5 V output does, and the owner planned to put a load on the 5 V output and measure again.
4. Watch the serial console and the status LEDs as the machine starts; see SGI Personal Iris Troubleshooting Guide.

Related pages

• SGI Personal Iris
• SGI Personal Iris General Maintenance
• SGI Personal Iris Troubleshooting Guide
• SGI Personal Iris Documentation
• Capacitor Failure Symptoms
• Recommended Tools