Anyone that read my ‘working to not working in one simple step’ post may have wondered what I did to solve the problem.
It turns out that although these crazy server motherboards have all these slightly different PSU connectors on them, when in reality, they’re just an ATX mothermoard. Admittedly not everything worked, but I had enough working to know that it really was the old PSU that was the problem rather than the new motherboard.
To make this work, I had to understand what the various other connectors on the board are actually for.
The server motherboard I have has the following PSU connections:
- 24 pin ATX power connector
- 4 pin 12V PWR connector ‘to provide adequate power to the system’
- 8 pin CPU PWR connector
A normal desktop PSU has the following connectors:
- 20 pin ATX power connector
- 4 pin 12V PWR connector
The 20 pin ATX connector pinouts and 20 of the 24 pins of the ATX socket on the motherboard pinouts match up, which is what I was expecting. Rather helpfully, the 20 pin conector even fits perfectly into the 24 pin ATX socket on the motherboard if you line up the correct parts. Obviously four of the pins in the socket have nothing going into them, but it seems to be that they’re just used for additional power feeds. I hoped they weren’t required to at least turn the motherboard on for my testing.
The 4 pin 12V power obviously fits into the 4 pin 12V power socket on the motherboard.
So at this stage, I have nothing connected to the 8pin CPU PWR socket. I hoped that this would still let me turn the system on, but unfortunately it doesn’t. According to the server motherboard manual, the CPU PWR connector is just 4 Ground connections and 4 12V connections. I tested the various CPU PWR socket pins with a multimeter and it seems that two of the 12V pins connect together on the board and the other two connect together on the board. But not all four 12V pins are connected. This suggests that 4pins were for CPU PWR to one CPU and 4 pins were CPU PWR to the other CPU.
Now again, working on assumption, if you need 12V CPU PWR what on earth are the additional 12V PWR lines/socket for? I’m sure when this socket was introduced a number of years ago onto desktop motherboards it was to provide additional power to the ‘power hungry’ new CPUs that had been released at the time, was it not?
Seeing as the 12V PWR and the CPU PWR are all 12V/GND combos, I unplugged the 12V PWR and tested whether it conneced up to any of the 8 pin CPU PWR connector. Needless to say, it plugged straight into the first four pins (presumably for CPU0). I checked the motherboard manual against the colours of the wires going into each pin and the yellow wires were connecting to the 12V pins and the black wires to the GND pins. So it all made sense in my head.
So at this stage, I have a motherboard, 1 CPU installed into CPU0 socket, and two sticks of RAM (the setup requires memory to be installed in pairs). I have the 20 pin ATX power connector plugged into the 24 pin ATX socket. And the 4 pin 12V PWR connector plugged into the first 4 pins of the 8 pin CPU PWR socket.
I bridged the pins that a power on switch should connect to with a small screw driver…. And the system powered up!
So testing my server motherboard with a desktop PSU was actually pretty simple once I thought about it.
One thing to note… As we only hooked up to four of the pins in the CPU PWR socket. Installing the second CPU into the CPU1 socket. The system powers on but never POSTs. This kinda makes sense as the second CPU doesn’t have its CPU PWR connections.
But yeah… I’ve now invested in a new PSU for the server… I paid additional money for a dual redundant PSU caddy, one redundant PSU (yeah I know… only one, just in case the testing i’d done above was telling me lies!). I now have a working new server.