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Can PSU have just a bad CPU power connector?

Last response: in Components
August 18, 2010 6:29:53 AM

This is my second build. My first one was four years ago and went just fine. At the time, everything was new, and I was able to plug and play without any issues at all. Now that my PC is getting long in the tooth, I've decided to upgrade
many of the components. The case, PSU, video card, and SATA HDD are the same as my old build - so as far as I know, they are known good components. I purchased an ASUS P6T motherboard, an Intel i7 920, a Corsair liquid cooler for the CPU, and a set of 3 1GB DDR3 1333mhz DIMMs from Crucial (they are on the ASUS approved vendor list in the manual).

I spent a day taking the old one apart and putting the new one together. Power on - no POST. Then I start to troubleshoot for the next few weeks. I get the no memory beeps when I remove all components and DIMMs. I've tried a single stick of RAM in every slot and each of the three sticks on their own. Any time I have a stick of RAM in place, I get no sound on power up. The fans spin, the lights turn on, the DVD drives spin, but no beeps to indicate no VGA detected. I've called tech support twice, and have since RMA'd both the motherboard and CPU with the same symptoms each time. I've worked through the no-POST-steps-to-do-before-starting-a-thread without success. The one thing I haven't tried is breadboarding. I don't think there's a short because the standoffs, motherboard tray, and case are the same as my old ATX build. I've tried resetting the CMOS several times with no luck. Never any video output or no-VGA beeps.

The one thing that has changed, is that I've had to swap out the 4-pin CPU power cable for the 8-pin one on this new board. Could my 8-pin socket on the PSU be dead? It's a 550 watt PSU. If it was underpowered, it would at least be able to POST with no drives, right? The only thing I could think of is that maybe all three RAM sticks are bad and any time I put one in, it prevents the motherboard from getting past the memory check to the VGA check.

The motherboard manual says that for a "fully configured system" I should have something in the 700 to 1000 watt range. I presume "fully configured" means all PCIE and PCI slots are filled and I have 6 DIMMs installed. I'm not anywhere near that loaded, even if I had all my drives and components installed.

My power supply is this one:

I've noticed something else as well. I get the same results when I completely disconnect the 8-pin CPU power from the motherboard. It could be that my PSU just isn't supplying any power to my CPU. I wish I had another power supply to test it out.

What else could it be?
a c 104 ) Power supply
August 18, 2010 7:34:49 AM

Its possible your 8pin (Or just the 8pin cable itself) is a dud,
best way to find out imo is get a multimeter and check each wire,
or if you cant yourself, get a local repair shop to test the psu for you
a b ) Power supply
August 18, 2010 10:54:07 AM

wow, thats a fancy pants PSU, ive never heard of that brand before though. Do the multimeter thing as per the above post, or I would look closely at the power connectors and make sure they are not physically damaged. You can also get a 4 to 8pin converter fairly cheaply from most computer stores, try that.
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August 18, 2010 11:34:36 AM

Ultra are not a good brand, so I'm going to assume thats a bad PSU. what GPU are you using?

coudl well be the PSU failing to supply the system. my crappy CM PSU was unable to power a 4890 based system, when it technically should have been overkill. and ultra are worse than CM from my experience.
a b ) Power supply
August 18, 2010 7:17:39 PM

ultras are overpriced crap.
a b ) Power supply
August 18, 2010 11:07:54 PM

now ive heard about the quality of the PSU, I would suggest opeing it up and looking for leaky capacitors, if you are confident in doing that.
a c 144 ) Power supply
August 19, 2010 6:18:30 AM

Opening up the PSU will void any warranty you have.

It would be unusual for all eight wires on the 8 pin CPU power plug to be bad. You can test this simply by using the 4 pin CPU power plug. For a short time, you will be OK.

Unless one of the memory sticks was shorted, bad memory would still generate BIOS beeps.

First rule of upgrading: when things go wrong, back up to the last known good working point. Your old system worked before upgrading, right? Breadboard it. If it doesn't work, you probably have a bad PSU.

By the way, second rule: if possible, change one component at a time.

jsc's third rule: breadboard a motherboard/CPU/RAM combination before you go through the work of installing it in the case. Takes just a few minutes, and it's nice to know that you are installing parts you tested.

In fact, I go one step farther. I breadboard all my new builds, including installing Windows, drivers, safeware, and connecting the system to the internet.

August 26, 2010 12:23:43 AM

OK. I tried backing it up to my old system configuration - no new parts. The system booted up to Windows, but was really unstable and froze. That happened twice before I gave up. I figure that maybe I handled the motherboard a little rough after removing it since I figured it was done and I wouldn't need it again. But at the very least, that showed that the 4-pin CPU power worked as well as the rest of the PSU connections.

I tried the 4-pin connector for the CPU power (the new motherboard came with a cap for the other 4 pins), but I had the same results as with the 8-pin. I don't have the tools or another PSU to swap, so I probably need professional help for that.

My video card is this one:

It doesn't require it's own power connection, but then again, I don't even get the no VGA detected beep code when it's disconnected.

September 2, 2010 4:52:57 PM

Professional techs have not been able to diagnose my system either. From what they can tell, there's no reason why it shouldn't be working in it's current configuration. So now what do I do?
Since I don't know what's wrong, how can I fix it? Should I just buy a different model of motherboard and try again?
a c 144 ) Power supply
September 3, 2010 12:55:06 PM

Work through our standard checklist and troubleshooting thread:
I mean work through, not just read over it.

Breadboard - that will help isolate any kind of case problem you might have.

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. Remember, at this time, you do not have a graphics card installed so the load on your PSU will be reduced.

If no beeps:
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 the system beeps:
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. It's possible that you can pass the POST with a defective video card. The POST routines can only check the video interface. It cannot check the internal parts of the video card.
September 3, 2010 3:43:07 PM

I had the techs at the shop check the PSU from top to bottom because I don't have a known good one to swap with, and I don't have a voltage meter to test with. They tell me it runs like it's brand new.
I definitely get the no memory beeps when I have no sticks installed. I do not get the no video card beeps. I just get silence and no POST. It doesn't matter which stick I used (I've tried all 3), and it doesn't matter which slot I use (I've tried all 6), I still get no beeps when I have a stick of RAM in but no video card.
October 19, 2010 9:50:17 PM

After working on this for a couple months, I finally got it. It turns out it was the RAM. Either the DIMMs were bad or they were incompatible (although I can't figure out why). They wouldn't let the board get as far as the VGA check. I bought a new DIMM (different speed, different brand) and it started right up and booted to windows.

Now I have new issues within windows, but that's probably a different thread. Thanks for the input along the way.
a c 144 ) Power supply
October 22, 2010 7:21:24 AM

Glad to help. That's what we are here for.