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Short circuit in mobo

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September 10, 2010 4:21:22 PM

hello guys... :) 
im having a serious problem in my desktop and looking for a suggestions and comments

my pc is dell optiplex 330 mini tower.

recently i have start to use this dell (kept away for more than 1 year) and i power on for few hours and everything looked fine. again after few days (yesterday night) i on the pc and start to make a network with my laptop. after connecting the network cable for about 10 miniutes (coudnt setup the network actually and after got only 2 successful pings it just down) pc just off and start to blink the power button in amber :(  (psu fan is also not working.) and i tried several time connecting and disconnecting the power source but no luck

today morning i started to look in the cpu.

finally i realized that psu is working fine. (by manually turn on psu by PSON) and all voltages are seems to correct. even, without connecting aux power connecter, psu become on (those days this dell pc just turning on once i pug it to wall bracket.) and then, power light become steady amber. but this time, CD rom is working and i didnt check wit HDD.

but whenever i plug the aux connector, psu not working...

so i guess mobo is short circuited.

is there any way to bringing up this pc without putting a new mobo???

i appreciate your comments, questions and suggestions

thnx


More about : short circuit mobo

a c 235 V Motherboard
September 10, 2010 4:29:36 PM

1) Do you have another PSU to test with in your system? It still seems to be your PSU has died and doesn't have enough juice to power on your system... (CD rom takes minimal power so not the best verification). It is more likely it died after one year than a motherboard.

2) Also, I would look to replace your CMOS battery, as it might have died too. Without getting any power source for a year, it could have been drained of power and finally kicked, which will keep the system from Posting.
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September 10, 2010 4:38:18 PM

no currently i dnt hv any system..
yes... CMOS was dead too and clock was resetted... but i didnt change.. thnx for reminding me... ill change right nw and let u knw.
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September 10, 2010 5:00:05 PM

sorryy.... changing the battery didnt help me. . :( (
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September 11, 2010 7:07:39 AM

changing psu also didnt help me...
any suggestions plss................
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a c 156 V Motherboard
September 11, 2010 9:16:28 AM

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 beeps 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. You do have a case speaker installed, right? If not, you really, really need one. If your case or motherboard didn't come with a system speaker, you can buy one here:
http://www.cwc-group.com/casp.html

Make sure you plug the CPU power cable in.

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 motherbord 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...

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.
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September 11, 2010 10:07:41 AM

ok thnx for ur reply jsc... :) 
ill start work through it... then will post result here (will take around a day :D )
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September 11, 2010 12:11:13 PM

ok i done everything and here are the results.....

did breadboard thing with only CPU and mobo.(having a only onboard vga). i pluged only 2 psu sockets(main and aux sockets) , cpu fan, speaker, and front switch pannel.

when i power on, on beeps and no cpu fan working. even psu fan also not working
but when i remove only aux connecter and try to power on, psu become working. and voltages are correct...

when i change the psu, results are same. when ever i plugged aux connecter psu not working.


what is your idea plss????
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!