Weird No-Power Issue

July 24, 2010 at 22:29:36
Specs: Windows XP
Hey Guys,

Okay I'm new but I have done my homework, have read close to 100 threads now before posting.

First off, here is my specs (yes I know it's old):

MSI K8N Diamond Plus
AMD Athlon 64 3700+ Socket 939
OCS Gold Edition PC4000 Dual Channel DDR(500mhz)
Silverstone 560Watt (but more importantly, 38Amps on 12v rail)
2each Geforce 7600GT in SLI

Okay, now as I said I have done much research and think I have a faulty mobo, not positive though. I need to pinpoint the problem and also figured out WHY this happened.

My computer, when pressing the power button, starts up for 1 second then shuts off. All fans spin, etc, but no beeps (presumable because its only on for 1 sec). After this I see that the LED on the back of my PSU is red, when normally it is either Green or Orange. I have found out red might indicate circuit protection has been initiated.

Okay, so maybe I have a short.

I pull out the components to do a bench/breadbord test. I start with the bare essentials. I swap out ram sticks, one at a time to see if they might be bad. I try another socket 939 processor. Still same problem, starts up for 1 sec then immediately shuts down.

I try jumping the pins for the power switch, thinking the switch might have been faulty, but it is not, same problem. I try jumping the 'green' wire and a ground on the 24 pin mobo connector, to test the PSU. It comes on and stays on until I disconnect these jumped pins. So it would appear the PSU might be okay (was not a load test, but still...)

Now I am down to possibly the mobo, I inspected with a flashlight and magnifying glass, no bad capacitors, no burnt components that I can tell.

Thinking my next step is to dive into PSU testing with my multimeter, but I will have to read up on that first.

Here is the kicker: When I disconnect the 8pin CPU connector (the one that plugs into the mobo to give the CPU its power), when that is DISCONNECTED, then the computer will power up and stay powered on. Once plugged back in, however, and tried to start it does the 1sec on then dies thing.

So, i guess there might be short circuit in the cpu/mobo/psu wiring somewhere, just not sure where.

Seriously guys, anyone have any ideas as to what could this be?

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July 25, 2010 at 00:10:25
do u hear any beeps? U can try to use another psu and also test cpu, ram, v-card in another compatible system but iam positive the board is out.

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July 25, 2010 at 00:43:19
As I said in my above previous post, no beeps (I am guessing it is because the system is not powered long enough to get to that point, it turns on and shuts off in a second or less).

I have used 2 known good CPU's and it does not work so I believe that would eliminate that as a culprit.

I don't have other compatible parts readily available to swap out to test, and I don't want to buy a PSU just to see if it is bad, I need to find out what is wrong so I can buy the correct replacement part.

I agree that it does seem most likely that the mobo is fried, I just don't know how. It was working just fine and then nothing...

Something is shorting out the 12v rail I think, and tripping the PSU's circuit protection. But so many components share the 12v rail that it could be anything.

Although when I remove the 8pin CPU power connector and it works, that leads me to believe the short is related to that area....

Does anyone else have any similar experience with this?

I have found tons of threads with similar problems, but they all end without a resolution, people just don't come back on the forum to post what the outcome was...

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July 25, 2010 at 01:22:51
Unfortunately there isn't a way to tell whether you have a powersupply or motherboard failure without access to either a spare known good motherboard or PSU, unless you have a proper powersupply load tester. You may be able to pull the PSU and take it to a tech for testing.

Goin' Fishin' (Some day)

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July 25, 2010 at 10:14:12
Yeah, I guess what I could do is buy both online somewhere with a good return policy and then just send back the one I don't need... Just frustrating though, because part of me just wants to know what is wrong to satisfy my curiosity. I have gotten close to pinpointing it, but why is it with computer parts that you just throw them away when they go bad? Unfortunate that there is not more that can be done about repair.

I mean seriously, now if I need to purchase a new mobo, it will also mean purchasing basically a new setup (CPU, RAM, Graphics, etc etc) because they don't make the socket 939 now so I can't just buy a new mobo to fit my CPU, then buying a new CPU I will be severely ram-bottlenecked (ddr1 500mhz), then with new ram I will be very graphics constrained (7600gts are old, no pixel shader 3.0 or any new features...).

If this was a cheap motherboard I would probably just give up. But I LOVE my K8n Diamond plus, it is just so awesome. Overclocking, and plus that cool heatpipe from the SB to the NB....

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