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Motherboard bad?


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#1 rraa497

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Posted 24 January 2011 - 03:54 PM

I'm working on a computer that I got for free. The motherboard is an A780G M2+SE. The problem is when I plug it in and turn it on it does nothing. I searched and found the test for the power supply. I placed a jumper from the green wire to a black wire (20 pin plug) and everything turns on but as soon as I remove that jumper it shuts off again. Is the motherboard bad? or something else?

Thanks
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#2 MrBruce1959

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Posted 24 January 2011 - 04:27 PM

It sounds to me like your switch or switch wire my be bad.

You say if you power up the computer jumping the ATX power supply wires, the computer starts up, however using the computers power button on the tower has no effect.

you will have to locate which two wires create the power up circuit between the button on the tower and the connector to which connects to the motherboard.

If you have access to a VOM meter, you can set it to the Ohms range and check for continuity of the switch when it is pressed in, the meter should respond while the switch is pressed in. This will show whether the switch is bad or not.

If this switch proves to be good, you may need to check the motherboard for jumper labeled ATX and make sure there is a jumper on this two pin jumper. (Some older motherboards allowed use of either baby-AT or ATX power supplies, if you have both power supply ports on this motherboard, you would also have this jumper.

To lessen the confusion, I am providing a link to a web site which may help you with a better understanding of these circuits, this page will also offer you images and procedures you can try to properly diagnose your power to motherboard issues.

http://www.playtool.com/pages/psucompat/compat.html (Please use the links at the top of this page to continue your diagnosis, there is one page which shows the pin-outs and their use in various power supply connections)

Bruce.

Edited by MrBruce1959, 24 January 2011 - 04:29 PM.

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#3 rraa497

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Posted 24 January 2011 - 06:08 PM

Ok..... When I plug in the cord and push the on/off button nothing happens. But, if I use a jumper and power it up that way then push the on/off button on and take the jumper out it will stay on. I then can use the on/off button as normal. If I goto shut down or unplug the computer, then I have to do the same process over again. Any idea on that?

Edited by rraa497, 24 January 2011 - 06:14 PM.


#4 MrBruce1959

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Posted 25 January 2011 - 12:32 PM

if I use a jumper and power it up that way then push the on/off button on and take the jumper out it will stay on.


For clairification here, is this senerio above when you have the ATX 20/24 power connector disconnected from the motherboard and you have the pins jumpered (green wire to black wire) on the 20/24 power plug such as the one in image below? (note this image does not show the jumper in place.

Posted Image
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Edited by MrBruce1959, 25 January 2011 - 12:36 PM.

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#5 rraa497

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Posted 25 January 2011 - 03:41 PM

Yes. I place the jumper from the green wire to a black wire in the 20 pin plug then I plug the 20 pin plug in with the jumper in place. It powers up, i push the on/off button on (the light around the button lights up), then I take the jumper out and it stays on. When I shut it down I have to do the same steps over again to turn the computer back on.

#6 rraa497

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Posted 29 January 2011 - 12:36 PM

Any more informatin on this issue would be helpful.

Thank you

#7 dc3

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Posted 29 January 2011 - 02:03 PM

The on/off button on the case is a momentary switch, just like the old door bell buttons which would ring the bell as long as you kept the button pressed. On the motherboard there is a header, a series of pins which the front display and controls plug into. If you trace the wires back from the power switch to the header you can remove the two wires and use a screw driver to short the two pins together which will act as the switch. This should only need contact for a second or two for this to work. If this works then you have narrowed the problem down to either the switch itself, or the wires. This is where it would be best to use a Ohm meter to see if the wires and switch are good, as suggested by Mr.Bruce.

If this doesn't work, then you have a problem with the motherboard.

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#8 MrBruce1959

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Posted 29 January 2011 - 03:20 PM

I am providing a link to the BIOSTAR computer support web site for your model number below.
There are various downloads available at this page which includes PDF versions of your owner manuals.

http://www.biostar.com.tw/app/en/mb/driver.php?S_ID=372

I have downloaded a copy of your owners manual and will provide some information which should help you diagnose your problem shortly.

However if you click the blue MANUAL button on this page, a download will be offered in .zip form. Download the .zip file and unzip it to your desktop.

There are 3 Adobe Acrobat PDF format files in this folder that have very useful information including the pin-outs of all the connectors on your motherboard.

As I look at your motherboard image, I see we can eliminate the possibility of an ATX jumper I mentioned above, your motherboard only accepts the ATX type power supply. I provided that answer earlier without looking at your motherboard map first. So ignor that suggestion I made to you earlier.

You have a 16 pin connector on your motherboard which is located near your SATA connectors.
The motherboard should have numbers next to this connector which should show pins 1 and 9 on one side and pins 8 and 16 on the other side. To help you out a bit, pins 8 and 16 should be the ones closest to the edge of the motherboards corner.

Pin number 15 and 16 are your power on/off pins, this is the one your towers power on switch should be connected to. You can remove this connector and using a metal object such as a screw driver tip, you can briefly jumper those two pins. If your computer powers up successfully, you have just proved your momentary switch on your computer tower is faulty and needs to be repaired or replaced.

You also want to make sure the connection on the 4 pin ATX power connector from the PSU is connected and making a good electrical connection.

This 4 pin connector is located close to your CPU socket (the corner closest to your VGA port)

If you have any further questions, please feel free to ask.

Bruce.

Edited by MrBruce1959, 29 January 2011 - 03:27 PM.

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#9 rraa497

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Posted 29 January 2011 - 09:02 PM

I touched the two pins together and nothing turned on. So, I'm assuming this board is bad....? What board do you recommend that is close to this one that I can replace with?

Edited by rraa497, 29 January 2011 - 09:02 PM.


#10 MrBruce1959

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Posted 30 January 2011 - 04:11 AM

I touched the two pins together and nothing turned on. So, I'm assuming this board is bad....?


This could very well be true, since this connection basically sends a signal to the controller chip to power up the computer or power it down if that option is selected in the motherboard BIOS setup utility.

Now I want to add that a problem with your PSU could also cause this same issue you are having here.

Jumpering the green wire which is pin #16 to a black wire sends a by-pass signal to the PSU to power up, but issues with-in the PSU can cause a problem on the motherboard.

Please check this link for the pin-out chart for the MAIN 24 pin ATX power plug.
http://www.playtool.com/pages/psuconnectors/connectors.html#atxmain24

If it is at all possible, try using another PSU to see if the problem still persists. If it does, then you know you have an issue with the controller chip on the motherboard or a leaking electrolytic capacitor.

For diagnosing bad caps, check these three links below for ideas on what to look for. (Note: Bad caps can be replaced by the average home computer user, with a little knowledge of using a soldering iron.)

http://en.wikipedia.org/wiki/Capacitor_plague

http://pc-medic.blogspot.com/2006/10/leaking-capacitors.html

http://www.capacitorlab.com/visible-failures/
This site also has a page covering re-capping a motherboard, you can check it out at this link here.
http://www.capacitorlab.com/replacing-motherboard-capacitors-howto/index.htm

Hope this helps.

Bruce.
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#11 rraa497

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Posted 31 January 2011 - 03:40 PM

I double checked and tested the on/off button with a meter and it shows ok.

Just tested all of the pins and found pin 9 purple (VSB +5 volts) only shows + 4.1 volts. Every other pin is within the tolorence. Could this be a bad PSU?

I also checked the caps and everyone looks good.

#12 rraa497

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Posted 26 March 2011 - 10:25 AM

Getting back into this project..... can someone reply to my last post? Thanks

#13 MrBruce1959

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Posted 26 March 2011 - 06:00 PM

Hello, I have seen your situation is still a no go and no solution has yet to be found.

It is sounding more like a bad solder joint or bad connector somewhere on the motherboard.

This is can be caused by stress or warping of the motherboard.

It may be located on either the 20/24 pin main ATX PSU to motherboard connector or the 2 pin connector that the tower's power switch connects to.

Repair would involve a close inspection of the solder joints using a magnifying glass or 5X powered jewelers loop.

A gentle rocking of the connectors will reveal a loose solder joint, but it may not always be easy to see.

My belief is that the bad connector to motherboard solder joint will be near the location where the green and black wires are connected, or where the case front power switch is connected.

You have requested earlier advice on what would be a good replacement for this motherboard if it is in-fact a bad motherboard.

In order to make suggestions to you, we would need to know what the highest dollar amount is that you are willing to spend.

What parts you have and if you want all of those to work with your new motherboard.

If your intentions are to replace the motherboard and to re-use everything you have in your present system, you need to list what you have, such as what CPU you have, the make and model number of your RAM.
Both of those will have to fit and be supported by your new motherboard, there are older motherboards offered on Ebay and http://www.newegg.com

You might very well find that your exact make and model number motherboard is still available in brand new un-used condition on one of those sites.

Bruce.
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#14 Suicide King

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Posted 26 March 2011 - 07:18 PM

Hello, I have seen your situation is still a no go and no solution has yet to be found.

It is sounding more like a bad solder joint or bad connector somewhere on the motherboard.

This is can be caused by stress or warping of the motherboard.

It may be located on either the 20/24 pin main ATX PSU to motherboard connector or the 2 pin connector that the tower's power switch connects to.

Repair would involve a close inspection of the solder joints using a magnifying glass or 5X powered jewelers loop.

A gentle rocking of the connectors will reveal a loose solder joint, but it may not always be easy to see.

My belief is that the bad connector to motherboard solder joint will be near the location where the green and black wires are connected, or where the case front power switch is connected.

You have requested earlier advice on what would be a good replacement for this motherboard if it is in-fact a bad motherboard.

In order to make suggestions to you, we would need to know what the highest dollar amount is that you are willing to spend.

What parts you have and if you want all of those to work with your new motherboard.

If your intentions are to replace the motherboard and to re-use everything you have in your present system, you need to list what you have, such as what CPU you have, the make and model number of your RAM.
Both of those will have to fit and be supported by your new motherboard, there are older motherboards offered on Ebay and http://www.newegg.com

You might very well find that your exact make and model number motherboard is still available in brand new un-used condition on one of those sites.

Bruce.


I agree with Bruce.

Although, Bruce, wouldn't it be a good idea to try and unplug all devices from the motherboard to make sure the problem is limited to only the mobo/psu/cpu? The reason I say this is because I've seen some WEIRD shortages before -- things which I would have never expected at first glance. Even stuff like a shortage inside the motherboard on an IDE port for the mobo, that was stopping a hard drive from spinning up... not that it is particularly related to this case. Just to eliminate everything else, we may want to give that a go -- just to be sure as a last ditch effort. What do you think?

Edited by Suicide King, 26 March 2011 - 07:19 PM.


#15 Darth sidious

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Posted 26 March 2011 - 08:20 PM

Try the psu in another pc if you have access with an equivalent power rating if it works eliminates it.
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