The Power Supply
We set out with a multi-meter and a little imagination and figured out a pinout of what was going where. The next day we got this confirmed when we got a pinout someone else had done. So now we knew what went where, now we needed to figure out where it was coming from?
(Click on the picture for a larger one)
(Thanks to whoever made this picture, which was supplied by brer.)
There is one standard AT power connection on the board providing power to the board and all of the built in stuff on it. That seemed simple enough, but what about all of the other stuff? There is a row of six 5 volt connectors that go to the individual VRMs (we think) for the processors and then a 3volt connector that provides power to other things. Seems this was ATX before ATX... so the electronics wizard told us to rewire a ATX power supply, and we did, starting with a single supply for testing. Investigations are ongoing to find out about tying multiple supplies together, but this first one will work to make it start up.
Note: It appears that all of the 5V and ground leads are tied together, both in a connector and between connectors. From talking to the wizard, it seems that this bad boy can draw so much current as to melt off a single trace!
Second Note: To clarify what we did with an ATX power supply, we cut off the ATX connector and solidered on an AT connector, making sure all of the colors matched up (AT orange goes to ATX grey). This left us with a few extra ground wires, orange wires (3.3V), a purple wire and green wire. We didn't use the purple wire, tied the green to ground (ON switch), and tinned the orange to place in the 3.3V connectors. Keep in mind, this is only for testing... ;-)
Next, as we draw closer to a functioning machine, how big a power supply becomes an issue. In the standard ALR case, 700 watts were available, with optional expandability to 1050 watts. That's a lot of power! To start to bring bring together an estimate, we have pulled the following from Intel's Pentium Pro Datasheet:
| Processor | Typical draw (Watts) | Typical 6-Processor draw (Watts) | Max draw (Watts) | Max 6-Processor draw (Watts) |
| Pentium Pro 150, 256k | 23.0 | 138 | 29.2 | 175.2 |
| Pentium Pro 166, 512k | 27.5 | 165 | 35.0 | 210.0 |
| Pentium Pro 180, 256k | 24.8 | 148.8 | 31.7 | 190.2 |
| Pentium Pro 200, 256k | 27.3 | 163.8 | 35.0 | 210 |
| Pentium Pro 200, 512k | 32.6 | 195.6 | 37.9 | 227.4 |
Other common components:
| D-Link DE-528CT PCI Ethernet Card | 2.5W |
| Cheetah 18GB SCSI Hard Disk(ST118202LC) | 31.5W startup (13W idle) |
| IBM 4.5GB Hard Disk(DDRS-34560) | 25.35W startup (5.3W idle) |
| Generic video card | 6W |
| Adaptec PCI SCSI card (AHA-2940) | 7.9W |
| VRMs | (>.84 efficiency. That is the total PPro watts * 1.2, worst case) |
| Plextor 6x SCSI cdrom | 29.65 worst case, 12.5 avg. |
So my current estimate is around 400 Watts of power, 600 if you are going to fill it with drives. The current optimum solution would be for 2 250-350 watt supplies tied together, which is what we are working on.
Our power-up tests involved a single 250 watt ATX power supply. This supply powered 4 200 Mhz Pentium Pro processors, 4 CPU fans, 96 meg of RAM in 8 SIMMS, the floppy drive, and PCI video and Ethernet card (the drive was on it's own supply). Using the ALR Infomanager utilities, it looks like this was the borderline for this machine. The 5V supply is dangerously low... so low, that moving the mouse in Windows 2000 caused it to drop more! On a positive note, this seems to indicate the 400 watts is quite close to the mark.
Update: The server we have assembled has a 445 watt power supply. The ALR Infomanager shows no drop in voltages with 2 hard drives, 4 processors and 8 fans.