Indigo Tendencies


A potential project for RetroChallenge:

To resurrect a Silicon Graphics’ Iris Indigo R3000 workstation by replacing it’s broken internal PSU with a custom cut-and-fitted PSU from a salvaged PC or Sun.

Difficulty Rating: can be done in the time available, assuming parts can be obtained.

Danger Rating: high – could easily let the magic smoke escape. Fortunately I have a spare CPU board for the Indigo, so blowing one away would not be the end of the world. On the other hand, blowing myself away would probably result in disqualification…

This project is not as easy as it sounds, for three reasons:

  1. The donor PSU must be able to source 25 Amps at +5V DC, 1 Amp at -12V DC and 6 Amps at +12V DC. It has been a long time (1995?) since mainstream PC PSUs could source that much current on the +5V and -12V rails.
  2. The donor PSU will need to be fitted into the original SGI PSU steel case, which has a totally unique shape and size.
  3. The SGI PSU also contains the workstation’s high-quality audio speaker and audio signal connection from the motherboard; this connection will need to be preserved or replaced when fitting the new PSU innards – the sound quality and capability is one of the main reasons for having an Indigo at all.

The first two issues will require finding a donor PSU almost as rare as hens teeth 🙂

PS: Why do this rather than just buy an original Indigo R3000 PSU? Well, although R3000 Indigo PSUs can still be bought (*new* sometimes), they were only manufactured from 1991 to 1993, and are all of such an age that (even “new”), the primitive capacitors and wire-wrapped inductors have deteriorated due to chemical action. These PSUs have a tendency to quit after a few weeks of use. In principle a PSU from an R4000 Indigo would work, would be a few years younger, and much less stressed in the R3000. However, such units are pretty rare and consequently expensive on a hobbyist budget.

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