SGI IRIS 4D Capacitor Replacement Guide
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The capacitors that owners have replaced in the SGI IRIS 4D twin-tower Professional IRIS machines (4D/50 to 4D/85) are in the LH Research "Mighty Mite" power supply in the base of the drive tower.[1][2] No schematic or service manual for the supply is known.[2] The other IRIS 4D lines have their own guides: SGI Personal Iris Capacitor Replacement Guide, SGI Indigo Capacitor Replacement Guide and SGI Crimson Capacitor Replacement Guide; for the Power Series see SGI Power Series.
Warning: the supply rectifies the mains into large reservoir capacitors at about 300 V DC, and its 5 V output is rated at 200 A. Unplug the machine, let the reservoir capacitors discharge and check them with a meter before working inside.[3][2]
The supply
[edit | edit source]jan-jaap gives the Mighty Mite in his 4D/70 a main +5 V output of 200 A; the unit in his 4D/50 is rated at 1000 W.[2][1] From his description of the 4D/70 unit and of a similar LH Research supply:[2][3]
- The input section has the mains filter coils, the rectifier diodes under a heat sink and two grey reservoir capacitors for the 300 V DC.
- The main 5 V output is built on two boards. One carries the pulse-width control and chopping, with about half a dozen white trimming potentiometers; the other carries the isolating transformers, rectifier diodes and output filter capacitors. Four 2N6678 transistors in TO-3 cases do the chopping.
- Separate sections make −5 V and ±12 V.
- Power resistors across the 5 V output capacitors provide a small load.
The control circuit is built from discrete analogue parts and calibrated with the trimmers. jan-jaap advises against replacing parts in it without a service manual, since the supply would probably need recalibrating afterwards.[2][3]
Capacitors reported
[edit | edit source]| Position | Parts | Finding |
|---|---|---|
| Main +5 V output (4D/70 supply) | Three 18,000 µF output filter capacitors | Tested good and left in place[2] |
| Mains input filter (4D/50 supply) | RIFA safety capacitor | Cracked; replaced[1] |
| 12 V output filter (4D/50 supply) | Output filter capacitors | Slight leakage suspected; replaced with several other output capacitors[1] |
Values for the other capacitors have not been published. Before ordering, record each one from your own supply: its position, capacitance, voltage, temperature rating, size and lead spacing, and mark the polarity on a photograph.
RIFA capacitors are metallised paper types used for mains filtering. jan-jaap notes that they absorb moisture, swell and crack, and can short and burst.[3] Replace any that are cracked with modern X or Y rated safety capacitors of the same class and value.
Removing the supply
[edit | edit source]The supply is in the base of the drive tower, behind an intrusion switch that trips the circuit breaker when the tower is opened.[1] It connects to the backplane through thick cables and sense wires, and to the mains through a harness from the breaker box with an external fuse.[2][1] jan-jaap found that taking the supply out and wiring it back in takes a long time; photograph the wiring before disconnecting anything.[2]
Checks after the work
[edit | edit source]- Load the 5 V output before switching on: the supply would not start without a load, and 10 A from an electronic load was enough. jan-jaap tested his supplies at up to 40 A.[1][2]
- Check the outputs for ripple and listen for whine or a steady tone. A 2.5 kHz oscillation on the +5 V rail went away when the sense wires were disconnected.[2]
- Refit the supply and power up the chassis with the card cage empty, checking that the fans run.[1]
- With the boards fitted, set the output so that the backplane reads 5.00 V. jan-jaap measured 50 mV of drop between the supply terminals and the backplane.[2]
See the troubleshooting guide for supply faults.
Related pages
[edit | edit source]- SGI IRIS 4D
- SGI IRIS 4D General Maintenance
- SGI IRIS 4D Troubleshooting Guide
- SGI Personal Iris Capacitor Replacement Guide
- SGI Crimson Capacitor Replacement Guide
- Capacitor Failure Symptoms
- Recommended Tools
References
[edit | edit source]- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 "Professional IRIS 4D/50, Clover 1 graphics", IRIX Network forums, jan-jaap and others, June to July 2025, forums.irixnet.org. 4D/50 supply: location, rating, RIFA capacitor, output capacitors, start-up load, intrusion switches, mains wiring.
- ↑ 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 "Looking for help with a Professional IRIS", IRIX Network forums, jan-jaap and others, December 2018 to February 2022, forums.irixnet.org. 4D/70 LH Research supply: 5 V section and its capacitors, chopper transistors, adjustments, sense wiring, bench tests.
- ↑ 3.0 3.1 3.2 3.3 "LH Research - research", IRIX Network forums, jan-jaap and others, April 2022, forums.irixnet.org. Layout of an LH Research supply, RIFA capacitors, control circuitry.