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Replaced a failed power supply and now no video

  • Gigabyte
  • Power Supplies
  • Video
  • Motherboards
Last response: in Motherboards
December 31, 2010 5:16:15 AM

My motherboard is the GIGABYTE GA-P35-DQ6 LGA 775.

I recently replaced a failed power supply (RaidMax RX-500-S) with a new Corsair CMPSU-650TX. The CPU fan and case fans turn on; however, I get no video. I’ve tried two videos cards and no video. I’m sure they both work.

This primary difference between the old and the new power supplies is that the new power supply has an 8 pin connector that connects to the ATX_12V_2X (labeled number 1 in the manual) on the mother board and the old power supply has a 4 pin connector that connects to the same. Naturally, I have to connect the 8 pin power supply to this connector and the old power supply had the 4 pin connector and it worked fine.

I noticed that some of the capacitors on the video card become extremely hot, too hot to touch.
Is there too much power being delivered to this connector?
Could I modify the power supply by cutting two of the yellow 12 volt wires?

Thank you

More about : replaced failed power supply video

December 31, 2010 9:14:04 AM

I've read in my manual that you should only connect a 4-pin to that connector.(the one next to the cpu) and NOT 2 4-pins. You may have cooked your CPU by doing that.
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December 31, 2010 12:31:16 PM

Corsair PSU's use a "4+4" CPU power plug instead of separate 4 and 8 pin connectors. Your motherboard has an 8 pin connector. You have 8 pins available. Use them. You did not cook your CPU by plugging in the complete connector.

Here's your problem: you said the old PSU failed. Right now, you have no idea if the PSU died by itself or if it took any other components with it. If it did take something else with it, it is probably the motherboard or video card and not the CPU.

Do not modify your PSU by cutting wires. It isn't neccessary and you will void and warranty on the PSU.

If our standard troubleshooting guide (the one mosox refered you to) doesn't help, try this:

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.

stingstang, I doubt if that is exactly what your motherboard manual says. Assuming that you have a Gigabyte motherboard (after all, you are in the Gigabyte forum :) ),
here's what my three G'byte manuals (EP45-UD3P, EP45-UD3L, EP35-DS3P) say:

Use of a power supply providing a 2X4 12V power connector is recommended by the CPU manufacturerwhen using an Intel Extreme Edition CPU (130W)."

And that is all it says. If Gigabyte had wanted you to use a 4 pin connector, that all they would have put on the motherboard - like my GA-G41M-ES2L.

Hey, what can I say. I like G'byte motherboards.

December 31, 2010 2:31:09 PM

Thank you all for your help; great info here.

When my system completely went dead last week, I heard a loud pop (no smoke). I did the paper clip test (green to black wire) on the old PSU and sure enough, it’s dead. I verified that the new PSU works via the same test. I do in fact have a speaker on this MOBO. I took the MOBO out of the case and removed the CPU. I looked for areas of burn marks on the front/back of the MOBO and CPU; found nothing suspicious.

I reinstalled the CPU, connected the 24 pin and 8 pin connector, and 1 case fan. The fan spins (including the PSU fan) and I get no beeps. Moreover; the CPU does not even get warm.

I think I have a dead MOBO and/or a dead CPU.
I’m open to suggestions or thoughts.

Thank you,