Dead Indigo PSU, ATX?
It’s been a few weeks since I could really do anything with the Indigo. After a global search for a SCSI2SD board (they are apparently suffering due to supply chain) I found a used one on eBay that was located in the Czech Republic.
It finally came a few days ago, I did my usual configuration of a CDROM drive and a Harddisk on the SDCard, copying the IRIX 5.3 install image to the CDROM part of the card, and everything looks like it was going according to plan.
I plugged the SCSI2CD board into the disk drive back plane, threw the power switch, and…. the computer blinked helplessly and died. Total power supply failure. Err, that’s not good.
I disassembled the Indigo and then took the power supply apart. I couldn’t see any obvious issue; its usually a capacitor that gives up after 30 years, but you can generally see which one fried. Not so much here. I contacted my friend with the SGI Salvage place, but he wasn’t too confident of any of his remaining ones. I was leaving on a a short vacation, so I just pondered it for a few days.
After some research, poolside, I got the idea to try using an off-the-shelf ATX power supply (PSU) for build your PC types. It quickly became obvious by reading the specs that the Indigo uses a superhuman 34A of +5V DC current plus more normal’ish amounts of +12 and -12V.
Looking at modern PSU’s it became obvious this was only going to work with a high-end ATX PSU. The largest +5V DC I could find was 30A at +5V, and I figured it was probably fine as my Indigo has base graphics, so probably comes in way under the 34A rating. It’s important to note that I wouldn’t have tried any of this if the Indigo didn’t have such a huge bay available for the huge ATX supply.
I ordered a Corsair 1200HX supply on vacation and when I got back it was waiting for me. It took me the better part of a day and half to figure out the wiring between the Indigo, which is in no way standard, and the ATX connector, which is a standard. Miswiring a power supply that supplies 36A is not something you want to do, so I really took my time double checking everything along the way.
Much to my surprise, I got it mostly correct the first time. The Indigo would boot up to the ROM prompt. Occasionally the PSU would go into start-stop-start-etc cycle starting and stopping every second or so. It seemed random if it would happen or not. The ATX supply provides a signal that its power is “good” when the voltage stabilizes. The Indigo had a similar input where the PSU could communicate if its power was “good”. Theorizing that the cycling was an initial current draw issue, I connected the two, which I originally left disconnected.
So far, that seems to have fixed the problem.
I’ll post the cross-wire configurations soon. For now, I’m continuing with the IRIX 5.3 OS Install to see what other problems arise!