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Weird PSU?? Problem

Last response: in Components
September 30, 2010 2:36:53 AM

I sold my roomate my old computer since I built a new one. I sold it without a graphics card. He bought a graphics card and I had 2 power supplies. I have him an A-Power AK750. It worked fine. He installed vista ultimate and everything was going great. He shut it down to update the service pack and it wouldn't turn back on. It tried to turn on at least (about 1s then darkness). The indicator light is on at all times on the mobo, so it's getting power. I gave him a logisys 650W to test with and it worked ok until it was shut down. I reseated the RAM graphics card and all the plugs and it still did the same thing (turn on for 1s then down). I never had problems like this before.

I took the AK 750W and placed it atop the case and just plugged in the 24pin and the 4 pin connectors. It started right up multiple times. I unplugged the Logisys psu and tried the same thing to no avail. So we put the AK 750W back in and it worked fine everything is smooth.

Does this sound like a power supply problem? Both of those PSUs were used for testing before and were known good. What about a bad BIOS battery? Could that cause this?

I doubt it matters but here is the specs:
Phenom X4 940 NO OC
8GB OCZ Reaper DDR2 1066
500GB Seagate 7200RPM
GTS 450 1GB

More about : weird psu problem

a c 144 ) Power supply
a b U Graphics card
September 30, 2010 6:13:39 AM

I do not think a bad BIOS battery would cause this.

Work through our standard checklist and troubleshooting thread:
I mean work through, not just read over it. We spent a lot of time on this. It should find most of the problems.

If not, continue.

I have tested the following beep patterns on Gigabyte, eVGA, and ECS motherboards. Other BIOS' may be different.

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.

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.

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.