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Problem with 12V rail on Corsair 650TX

  • Power Supplies
  • Corsair
  • Components
Last response: in Components
April 17, 2011 1:28:05 AM

Recently, my Antec 350W PSU stopped working (as evidenced by the crackling sound when I pressed the power button), so I decided to buy a Corsair 650TX based on its awesome reviews. After installing the PSU and plugging in the 24-pin ATX and the 12V ATX v2.2 pins, I press the power button and nothing happens. The board is not shorted, because if I remove the 12V pin, the fans start spinning but the bios does not post. I wonder if there is any way I can troubleshoot the problem. Motherboard is a gigabyte ga-ep35-ds3l.

More about : problem 12v rail corsair 650tx

a c 144 ) Power supply
April 17, 2011 12:42:03 PM

The following is an expansion of my troubleshooting tips in the breadboarding link in the "Cannot boot" thread.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different, but they all use a single short beep for a successful POST.

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

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.

Make sure you plug the CPU power cable in. The system will not boot without it.

I always breadboard a new build. It takes only a few minutes, and you know you are putting good parts in the case once you are finished.

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:
Running fans and drives and motherboard LED's do not necessarily indicate a good PSU. In the absence of a single short beep, they also do not indicate that the system is booting.

At this point, you can sort of check the PSU. Try to borrow a known good PSU of around 550 - 600 watts. That will power just about any system with a single GPU. 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.

A way that might be easier is to use the main power plug. Working from the back of the plug where the wires come out, use a bare paperclip to short between the green wire and one of the neighboring black wires. That will do the same thing with an installed PSU. It is also an easy way to bypass a questionable case power switch.

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, long single beeps, or series of short beeps indicate a problem with the memory. If you get short beeps verify that the memory is in the appropriate motherboard slots.

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.
At this point, if the system doesn't work, it's either the video card or an inadequate PSU. Or rarely - the motherboard's PCIe interface.

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.
April 17, 2011 12:51:58 PM

Reviewed that document, but I've already taken all those steps as standard troubleshooting. The PSU is brand new, but the system does not beep. Chances of an Antec PSU frying my motherboard after going out? I thought quality power supplies had failsafes to stop that.
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April 17, 2011 12:55:13 PM

Since I've basically narrowed it down to a problem with the 12V rail on the motherboard, is there any way to test whether or not its shorting/burned?
April 17, 2011 1:03:06 PM

While we're at it, before I buy a new motherboard, I'd like to make sure the PSU failure didn't damage my CPU as well. Is there any way to test without a second board/cpu?