ATX 12 V (CPU) power cable trouble

Hi y'all

I'm not getting into BIOS, so I figured it's the CPU not getting power and the cpu fan wont spin unless I put it in power_fan.

The odd thing is I managed to installed Windows 7 a few days ago (with cpu fan in cpu_fan), but quickly got freezes and the system would turn off.

I have a Fractal Design Newton R2 PSU and a ASUS M4A89GTD PRO/USB3 motherboard.

PSU manual says: Connect the 4-pin cable (also called a P4-cable) to the motherboard . If your motherboard instead has an 8-pin socket, connect the 8-pin (also called EPS12V-cable) cable to it.

Motherboard manual says: Do not forget the 8-pin EATX12 V power plug; otherwise the system will not boot.

Okay so my EPS12V cable fits nicely into the EATX12 V pin, but the system wont get into BIOS, I'm not sure it even posts, I don't have a speaker. But the PSU manual mention a P4-cable and I don't have that, unless the EPS 12v cable really is 4+4 pin, but it's not obviously easy to bend before I know I'm right. There was not other cables that followed which are 4pin or 8pin.

ALSO the 8 pin cable do not have the same squares/holes as the the EATX12v pin. It does not look like this:

Instead it has a:

cable in link has



The motherboard is currently out of the case, resting on the pack it came in.

Thanks for reading! :wahoo:
6 answers Last reply
More about power cable trouble
  1. Okay I found out I have a 4+4 pin +12 volt power cable, but if I connect only one 4 pin there's not difference. Fan wont spin on cpu_fan and no BIOS. I'm pretty sure it's not the memory sticks, the motherboard has flashed red lights at me when they have been improperly installed.

    BUT why don't I get any power??
  2. Have you read the mobo manual, and make sure everything is correctly connected? For example : does it need only 1x4 or 2x4? 20 or 24 pin? 6 pin PCIe to your GPU? Where to connect the proc fan and other fans? etc. etc.?
    Power on switch of the back of the PSU?
  3. Could be bad PSU or bad motherboard.

    You have worked through our standard checklist and troubleshooting thread:
    yes? I mean work through, not just read over it.

    Breadboard - that will isolate any kind of case problem.

    The breadboarding thread has a paragraph about how to build and test a PC in stages.

    Breadboard with just motherboard, CPU & HSF, case speaker, and PSU. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:

    You can turn on the PC by momentarily shorting the two pins that the case power switch goes to.

    You should hear a series of long, single beeps indicating memory problems.
    Silence indicates a problem with (in most likely order) the PSU, motherboard, or CPU.

    At this point, you can sort of check the PSU. Try to borrow a known good PSU. If you cannot do that, use a DMM to measure the voltages. Measure between the colored wires and either chassis ground or the black wires. Yellow wires should be 12 volts. Red wires: +5 volts, orange wires: +3.3 volts, blue wire : -12 volts, violet wire: 5 volts always on. Tolerances are +/- 5% except for the -12 volts which is +/- 10%.

    The gray wire is really important. It should go from 0 to +5 volts when you turn the PSU on with the case switch. CPU needs this signal to boot.

    You can turn on the PSU by completely disconnecting the PSU and using a paperclip or jumper wire to short the green wire to one of the neighboring black wires.

    This checks the PSU under no load conditions, so it is not completely reliable. But if
    it can not pass this, it is dead. Then repeat the checks with the PSU plugged into the computer to put a load on the PSU.

    If it looks like the PSU is good, install a memory stick. Boot. Beep pattern should change to one long and several short beeps indicating a missing graphics card. Silence or long single beeps indicate a problem with the memory.

    Insert the video card and connect any necessary PCIe power connectors. Boot. At this point, the system should POST successfully (a single short beep). Notice that you do not need keyboard, mouse, monitor, or drives to successfully POST.

    Now start connecting the rest of the devices starting with the monitor, then keyboard and mouse, then the rest of the devices, testing after each step.
  4. Hey, thanks for replies

    Unfortunately I don't hve any of that equiptment, but there's a store down here which repairs computer who probably does. If I'm lucky I can borrow from them.
  5. I borrowed an old 280W PSU and the same thing happens. Fan starts, but nothing else. Sometimes I can't shut off without turning the PSU switch and sometimes it shuts off by itself. He didn't seem to have a system speaker.. I also noticed I have to have a few more stuff connected, such as chassis fans, for the PSU to give power. How would I know the CPU is not damaged?
  6. bump
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