X58 motherboard works fine with a GPU, does not work without one. Any way around that?

[artlav]

So i got a Nehalem CPU i wanted to keep running for sentimental value, but i also didn’t want to have another big black coffin sitting around, so i looked around for a small LGA 1366 motherboard. There weren’t any mini-ITX ones, but i did find a microATX one - Machinist branded, X58 chipset. Good enough.

The board worked just fine, the CPU is still alive and well and performs as expected.

It draws 20-40W depending on the load, and peaks out around 60W.

With a GT 710 plugged in, that is.

What i wanted is a small headless box, so once everything was checked and configured, i removed the GPU and tried again.

Nope. It would draw 70-90W continuously for about the same 20 seconds as it would normally take it to boot, then drops down to 30W for a second, then power cycles. Again and again. No signs of it getting into Linux either.

I’ve looked around the BIOS, tried things like “Headless mode” under ACPI settings, to no effect.

It’s not the end of the world, i can spare an old GPU for the project, but it’s not as nice.

So, do anyone have any clues as to why an X58 motherboard would draw way more power than normal and refuse to work without a GPU? Am i missing something obvious?

[artlav]

Ok, further experiments revealed the problem.

I tried various cards to see if it would boot up with something other than a GPU in the slot. No effect.

Then i gave up, plugged in the GPU, plugged an HDMI dummy plug into it and tried to boot it up…

Same issue of 90W and power cycling!

Long story short, the 150W picopsu i was running it from wasn’t quite enough to power the board through spikes of full load during boot, but when something else is plugged in that provided an extra return path for the current to go through, bypassing both it’s overcurrent protection and the meter i had it plugged through.

So when it was “running at 20-40W”, it was actually running at way more than that. In retrospect, “TDP of 130W” CPU running at 60W full tilt should have clued me in.

TL;DR: It’s not a power issue. It can’t be a power issue. It’s a power issue.