No Power On and the 5VSB Voltage

[owensdj]

I'm trying to figure out why a computer will no longer power on. I connected the Antec 430W TruePower 2.0 unit to a power supply tester unit. The only possible problem I saw was that the 5VSB was jumping around between 4.9 and up to 5.3. The tester would beep sometimes to indicate an error. Could 5VSB be the reason the computer won't power on? I tried the power supply on another motherboard-processor-memory combo and it powered on fine, but the test board was only 20-pin ATX whereas the problem system is 24-pin ATX.

 

[drjman]

If the power supply works in another setup...it works. Your motherboard is pretty suspect now. 20 pin and 24 pin don't really matter as long as you hook the hard drive up. That antec should have no problem with either.

 

[owensdj]

drjman, thanks for the reply. The problem system is a 2.93GHz P4 but test system that powered up was just a 1600+ AMD Athlon, so I was thinking the power supply might be having trouble supplying the current the newer motherboard-CPU needs to power up. I've read that not having 720mA of current on the 5VSB line can cause some systems to fail to power up.

 

[robisbell]

if the motherboard requires a 24 pin PSU, then that's what you need. I would recommend you get a good quality 500 or 550 watt psu.

 

[owensdj]

robisbell, yes the system that won't power on does require a 24-pin PSU, It has a 430W Antec one in it now. I don't want to get another power supply if that's not what's causing the system to be unable to boot.

 

[robisbell]

I believe it is the issue.

 

[cubby1223]

Motherboards that have a 24pin power supply connector, they all state very clearly in the manual that a 20pin power supply is fine. Well, shouldn't say all, though I have not yet see one that demands a 24pin power supply.

Anyways, to the point of this thread, three things are required to power on a computer, the power supply, motherboard, and cpu. You don't need memory to power on a computer. Cpu is never the problem, cpus are by far the most robust equipment in the machine. You've tested the psu on another board and it worked. Leaves the motherboard as the cause.

You may want to get a new power supply to be safe - but it's not going to fix your dead motherboard. That's what needs to be replaced.

 

[owensdj]

cubby1223, I did replace the motherboard. It also can't power on using the existing P4 processor and memory. I tried powering on without the memory modules. Same problem. So you're saying the 24-pin P4 motherboard should be able to at least power on using a 20-pin power supply?

 

[cubby1223]

Originally posted by: owensdj
cubby1223, I did replace the motherboard. It also can't power on using the existing P4 processor and memory. I tried powering on without the memory modules. Same problem. So you're saying the 24-pin P4 motherboard should be able to at least power on using a 20-pin power supply?

When you're saying "power on" do you mean it does absolutely nothing when you hit the power supply? Or it turns on but you don't get any video output? I'm talking about the former, when absolutely nothing happens, including fans that do not spin up. Motherboard, cpu, and psu are the only 3 things you need to turn a computer on. And the cpu is *never* the problem, can't stress that enough. Actually I've never tried turning a computer on without a cpu, I actually think it might work. But that's neither here nor there.

I have not personally seen a motherboard that had a 24-pin connector and does not work with a 20-pin power supply (you always have to plug in the extra 4-pin P4 connector, that's a different plug that is a requirement. If memory serves me, the extra pins are to supply additional power to the pci-e slot if necessary. But every pci-e card that draws a lot of power has another external power connector anyways. And if you use onboard video, the pci-e slot draws no power.

 

[owensdj]

cubby1223, by power on I mean nothing happens. No fans start turning and there is nothing on the screen from the motherboard. The power supply doesn't power on either. I'm trying it with just the motherboard, processor, memory, and the Power Switch connected to the motherboard. The board has onboard video. I've also tried to power on without the 2 memory modules, and I know the Power Switch works correctly.