Hollywood or Dust


As is often the case with hardware this old, my 1991 SGI IRIS Indigo R3000 will not start. Well, that’s not quite completely true…

Symptomania:

When pressing the power-switch, the fan did not spin, neither of the two SCSI disk drives spun up, the screen remained resolutely blank, and the cute Indigo power-on tune did not play (yes, really: 1990s SGI machines have firmware that plays a short melody when the power-switch is pressed, before any attempt to boot an O/S).

However, signs of primitive life were there – the LED on the CPU board lit up yellow, indicating firmware power-on self-test is running, but it should then go green, which it just didn’t.

The LED on the external Ethernet AUI adaptor (remember those?) also wasn’t illuminating, which actually was rather a clue to the real problem, although not one I was aware of at the time.

Others have noted that on the R3000 Indigo, hot-replugging the CPU board can sometimes kick recalcitrant machines into life, so it was worth a try at this point… but didn’t make any difference. And no, it didn’t result in piles of smoke, either.

Inspection One:

Visual inspection of the CPU board (including checking for bent pins, blown or leaked capacitors, burned-out traces, and so on) revealed that it looked in fantastic shape. Multimeter also revealed that the on-board 3.6v IDPROM battery was good.

The graphics board also showed no sign of damage or rot. The backplane appeared likewise – no visually obvious problems there either.

Ripping Out:

Initially I thought that the SCSI disk drives might be suffering from stiction, so I removed them, installed them in an external powered SCSI enclosure, and tested that they spin-up when externally attached to my SPARCstation-10… they sure do.

With the drives powered externally and connected to the Indigo, they spin up, but the screen remains blank, but now the power-up tune does play, and the system might be trying to boot.

Second maneouver was to disconnect the keyboard, and use a serial-console instead: nope, no console messages there either. Not even corrupted, glitched characters. Nothing. This is another clue, although one that does not apply to all types of personal computer.

These Boots are Made for Running:

OK, so let’s remove the graphics board too. With just the CPU board in the chassis (drives in external enclosure, serial console), the system boots… Unfortunately, the ethernet still wasn’t working.

There is nothing left to remove, so now what?

Nekochan:

As is inevitable when dealing with old SGI kit, I ended up relaying my difficulties to the Nekochan Forums, a very informal online site for discussing all-things-SGI. For retrocomputing enthusiasts, it’s well worth a look.

Armed with my description of the system behaviour, one of the hardware experts there spotted the problem straight away: there was no 12V power getting to the components.

AUI adaptors need +12V to function, as do the SCSI disk drives. Also, 90’s SGI on-board serial-ports like 12V power, although it seems they can hobble along with lesser voltage. Nothing else on the CPU board requires 12V.

So that explains the problems.

The Job at Hand:

The obvious solution, buying another Indigo PSU, is a bit of a reach, current prices are around £200+. And even for new, unused, still-packaged units, it would still be 25 years old, and thus not necessarily “in good order”.

Thus it might be better (well, cheaper anyway) to attempt to repair the PSU. I’m not too keen to go poking around inside an ancient PSU with HTDC and 240V AC running through it, but needs must?

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