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ATX power connector problem

Last response: in Motherboards
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September 8, 2012 4:39:14 PM

Hi all. My computer won't power on so I took these steps:

1. Made sure it wasn't the power cable.
2. Tried another outlet.
3. Checked PSU switch to make sure it was set to on, but it doesn't have one.
4. Reinserted power cords into motherboard
5. Tested PSU with a multimeter and all pins that supply voltage are supplying the correct voltage
6. Shorted out pins 15+16 on the 24 pin motherboard cable and the PSU fan kicks in (as well as any other fans I connect)

I believe the power supply is working. When I connect the power supply back to the motherboard (and leave the power supply connected to the wall) the fans no longer spin. This makes me think there is something wrong with the connector on the motherboard. Is this correct? I hope not. Please tell me I am missing something and that there's something else I can do.

Edit: my motherboard is a G33T-AM model. I was unable to find it on the ECS site but it did list a G335-M2 model.
a c 1167 ) Power supply
a c 216 V Motherboard
September 8, 2012 6:19:13 PM

The ECS G33T-AM is an OEM version of the G33T-M2. Acer used that G33T-AM motherboard model.

The 24-pin ATX power connector doesn't supply any power to the CPU. The CPU gets all of its power through the 4-pin ATX CPU power connector.

Have you tried troubleshooting with a different power supply unit?

Have you tried troubleshooting with the motherboard outside of the case?
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September 8, 2012 7:17:18 PM

I know the 24 pin connector doesn't supply power to the CPU. It supplies it to the motherboard right?

Should the CPU even be involved at this point? My PSU worked when I shorted the pins, but when connected to the motherboard's connector, the PSU does not work.

I don't have access to another power supply. I have not taken the motherboard out of the case.
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Related resources
a c 1167 ) Power supply
a c 216 V Motherboard
September 8, 2012 7:25:54 PM

geiger9 said:
I know the 24 pin connector doesn't supply power to the CPU. It supplies it to the motherboard right?

Should the CPU even be involved at this point? My PSU worked when I shorted the pins, but when connected to the motherboard's connector, the PSU does not work.

I don't have access to another power supply. I have not taken the motherboard out of the case.

The 24-pin ATX power connector supplies power to the motherboard, expansion cards, USB ports.

Any short circuit in any expansion card or USB ports can cause the power supply to trigger its protection circuit.

When troubleshooting you need to reduce the system down to the bare essentials otherwise it becomes almost impossible to isolate the cause of the problem. Taking the motherboard out of the case with all external ports and non-essential expansion cards and peripherals removed allows you to determine if the problem is isolated to the motherboard.
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a c 1167 ) Power supply
a c 216 V Motherboard
September 9, 2012 1:35:59 AM

Looks like you're using an OEM power supply that doesn't have a main AC power switch.

Is there a power indicator LED on the motherboard that indicates that the power supply is providing +5VSB (i.e. +5V Standby) standby power to the motherboard? If the motherboard is not receiving any +5VSB power then you'll never be able to get the motherboard to turn on. The +5VSB part of the power supply is actually a separate linear power supply and is always on when the power supply is receiving AC power.

With the 24-pin ATX power connector and the 4-pin CPU power connector connected to the motherboard outside of the computer case you only need to momentarily short the power switch pins on the front panel header on the motherboard to emulate pressing the power button on the front of the computer case to cause the system to power on.
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September 9, 2012 11:31:32 PM

There is no power indicator LED on the motherboard unfortunately. However, one of the lights on the onboard ethernet port lights up (it's yellow).

Do you think I should try shorting the power switch pins even though the PSU fan isn't even spinning?
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a c 1167 ) Power supply
a c 216 V Motherboard
September 10, 2012 12:37:00 AM

geiger9 said:
There is no power indicator LED on the motherboard unfortunately. However, one of the lights on the onboard ethernet port lights up (it's yellow).

Do you think I should try shorting the power switch pins even though the PSU fan isn't even spinning?

When the system was completely working did the power supply fan spin even when you never pressed the power button on the front of the case?

By momentarily shorting the header pins for the power switch on the motherboard's front panel header you are emulating the pressing of the power switch on the front of the case. That is the only way to turn on the switched-mode portion (i.e. +3.3V, +5V, +12V, -12V rails) of the power supply that powers the motherboard unless you have the use of or access to a troubleshooting power switch that you can connect to those two pins.

The lighting up of the ACT/LINK or SPEED LEDs for the RJ-45 LAN port is usually a sign that the motherboard is receiving some power.
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September 10, 2012 4:17:48 PM

I'm not sure if the fan spun when the power was off.

Going to try shorting the header pins now. I'm hoping I don't destroy anything.
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September 10, 2012 4:37:10 PM

I shorted the two pins (6 and 8) momentarily, and.... nothing.
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a b V Motherboard
September 10, 2012 6:24:37 PM

Since your motherboard is outside the case, you can do the simple testing wth power supply, motherboard, and CPU heatsink fan. Just connect the power supply 24 + 4 pins to the motherboard and connect the CPU heatsink fan. Then, turn on the power supply by shorting the pins 6 and 8. If the CPU heatsink fan doesn't not spin, then the motherboard may be defective. If the CU heatsink fan spain, then you can try to plug in the hardware one by one. CPU--> memory --> hard drive --> etc.
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September 10, 2012 6:50:58 PM

ky_ecsusa said:
Since your motherboard is outside the case, you can do the simple testing wth power supply, motherboard, and CPU heatsink fan. Just connect the power supply 24 + 4 pins to the motherboard and connect the CPU heatsink fan. Then, turn on the power supply by shorting the pins 6 and 8. If the CPU heatsink fan doesn't not spin, then the motherboard may be defective. If the CU heatsink fan spain, then you can try to plug in the hardware one by one. CPU--> memory --> hard drive --> etc.


The CPU fan won't come on either. The light on the ethernet port no longer comes on either.

So I just tried clearing the CMOS using the jumpers. Now when I plug in the PSU, the fans on the CPU and the PSU come on, but there is a continuous POST beep.

Edit: I unplugged the PSU because the noise was annoying. I left it unplugged for about 60 seconds and when I plugged it back in, the fans no longer come on and there is no beep.

Edit 2: I had the PSU plugged in for a few minutes and it just randomly came to life! Still continuous beep though. This is weird.
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a b V Motherboard
September 10, 2012 7:07:04 PM

Do you mean that the system will come on automatically after plugging in the PSU? Try to take out the battery and unplug the power cord for couple hours. Then, reinstall the battery and turn the system on. If the problem still exists, it's possible that there is some shortage on the motherboard.
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September 10, 2012 7:12:18 PM

ky_ecsusa said:
Do you mean that the system will come on automatically after plugging in the PSU? Try to take out the battery and unplug the power cord for couple hours. Then, reinstall the battery and turn the system on. If the problem still exists, it's possible that there is some shortage on the motherboard.


A few times, it did come on automatically after plugging in the PSU. But now that has stopped.

I'm taking out the battery for a while to see if that helps.

Update 1 hour or so later: Reinserting the CMOS batter did not do anything.

Currently, the 24 pin and 4 pin connectors are plugged in plus the CPU fan. The yellow ethernet port light is on. Shorting the power switch pins does nothing. Going to leave it plugged in for a while to see if it randomly starts up. Also going to keep an eye on that yellow light.
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a b V Motherboard
September 10, 2012 9:45:20 PM

At this point, it seems that the motherboard may have problem. Please contact your retailer for the service.
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September 11, 2012 12:45:32 AM

After leaving it plugged in in the previous state for a few hours, I shorted out the power pins and it did turn on. However, I got the same never-ending beep code. I looked up the beep codes for AMI BIOS but there is nothing about a nonstop beep. I really don't want to have to buy another motherboard. So strange how these things happen. Computer works fine one day and the next, the motherboard is shot. How the heck?
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a c 1167 ) Power supply
a c 216 V Motherboard
September 11, 2012 3:06:59 AM

My suspicion still rests with a defective power supply.
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September 17, 2012 11:58:45 PM

I still have yet to test another power supply with this motherboard. When I do, I'll update this thread.
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November 13, 2012 6:15:04 PM

I have nearly the identical problem.

When trying to power up my computer, it generally will not power up. Every so often it will. I used this as a work computer and was able to get around this for a while by leaving it on. As long as we didn't lose power, or the computer shut down for another reason (which is rare), the computer would remain running and there is no problem.

Today I have tried many diagnostic steps. I have completely test my PSU with a multimeter w/o and with a load on it. The PSU voltages remained at acceptable levels.

I have pulled the mobo from the case, removed the ram and all connections except the following: the cpu and cpu fan remain connected as well as the 20 pin atx and 4 pin mobo power connections.

The bizarre behavior continues. It seems as though if time is allowed to pass (discharging perhaps?) and I try to power on the computer (regardless of the method - switch or short) that it will start and remain on. If I turn it off and try quickly to power on the computer again, it will not power up.

CASE CM|RC-330-KKN1-GP
MB FOXCONN M7PMX-S 775 GF7100
PSU ANTEC|BP500UB 500W
CPU INTEL|PDC E2180 2.0G 775
MEM 2Gx2|GSK F2-6400CL5D-4GBPQ

In the following steps will attempt to use another PSU and then I will pull out the cpu and test the bare system once again.

Geiger9 have you made any advances toward solving your problem? I'm open to anyone's suggestions. I'm thinking that I have a bad mobo. I don't know how to distinguish between bad mobo vs bad cpu.
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November 13, 2012 6:50:35 PM

Well,

I tried a different PSU and the system will power on with, what appears to be, no problems.
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November 20, 2012 1:15:01 AM

Hey everyone. I am still trying to locate another (free) power supply. A friend of mine loaned me his which he says worked fine but this PSU's fan would not even turn on when I shorted the pins on it.
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November 20, 2012 3:31:42 PM

Can you buy a PSU and test it? If it works, problem solved. If not, then take the PSU back.
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November 20, 2012 3:34:13 PM

My computer has been running fine since I changed out the PSU *knock on wood*. What I don't get is why the voltages all appeared normal, even under some load, but the unit was still bad. If anyone has an answer to that, I'd love to hear it for the sake of learning.

geiger9, I'd loan you my old one but I have no idea where you are and mailing it doesn't make sense. Hopefully you can find an old pc somewhere to pull a PSU out of or buy one like I posted prior.
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January 10, 2013 3:32:51 PM

Sorry for such a late reply but I figure it's better to provide closure to the thread.

I bought a new power supply (finally) and now everything is working fine.
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a c 1167 ) Power supply
a c 216 V Motherboard
January 10, 2013 4:40:53 PM

So my suspicion has been confirmed.

Thanks for coming back and posting your solution.
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January 14, 2013 5:16:05 AM

Bad capacitors can cause excessive voltage drop under load.
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!