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Can't get it motherboard to post

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December 10, 2010 3:32:53 PM

Hello, I'm currently working with my older computer when lately its pretty starting show its age and is having problems even booting into windows, my original idea of what is wrong is the motherboard since it is nearly 10 years old (Asus a7n8x deluxe) and the compasitors have started leaking.


So a few days ago i got a old computer from a relative that happens to use the same motherboard except in better looking condition. According to him the power supply died and haven't been able to use it since but today i decided to test the motherboard, I pulled my 560w to test it but im coming up with a strange problem; the computer will turn on for a few seconds and then will power off, no beeps or anything, ive tried 3 different videos cards and 2 sticks of ram but no luck does anyone know what could be causing this or is it a bad motherboard?

thanks.

More about : motherboard post

a b V Motherboard
December 10, 2010 5:03:49 PM

Hmm, depending on how that PSU died, I suspect it might have damaged that motherboard. Though if it was never used after the incident, it can be hard to tell exactly if that is it or if it's something with your current setup.

Also: Is that 560w of yours new and/or at least in fair condition?
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December 11, 2010 8:58:06 AM

yeah, i recently purchased last year for my current pc but i have been having trouble with some of its components like the video card will not boot the power will just flick on and turn off with any pc its hooked up to (bfg 7300 gt i think)
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a c 156 V Motherboard
December 11, 2010 12:09:09 PM

Having another similar computer for parts can simplify your troubleshooting. You have identical motherboards, compatible memory, and compatible CPU's.

Work through our standard checklist and troubleshooting thread:
http://www.tomshardware.com/forum/261145-31-read-postin...
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.
http://www.tomshardware.com/forum/262730-31-breadboardi...

Breadboard with just motherboard, CPU & HSF, case speaker, and PSU.
This is where you should start. If you disasemble both systems and breadboard, it will not take you long to figure if you are wasting your time or not.

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.
http://www.youtube.com/watch?v=5FWXgQSokF4&feature=yout...

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 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.
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.
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