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Mobo Wont Post - CMOS Batteries Dying


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#1
HitmanInWis

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The other day one of my computers with a A8N-SLI Premium mobo simply died and wont come back on. When I flip the power switch on the back of the box, the fans (including CPU) and everything in the box come on, but the mobo never posts. No video, no beeps, nothing. CD player wont open if it is connected to the mobo - I believe again b/c the mobo hasnt posted. This mobo is supposed to have audio messages for a failed post, but I'm not getting anything there either (I plugged in amplified speakers to the green audio out port). Only way to turn the machine off is to turn the PSU off - the power button does nothing, no matter how long I hold it. Replaced the CMOS battery and reset CMOS, still nothing. I did some searching around the net and found posts saying to strip the system all the way down to the mobo and CPU (with cooler), outside of the case. Did that, still nothing. People were saying that if the CPU was bad, the mobo should be telling me that, but it wasnt. Also, I tested the PSU using a multimeter, and it all checks out great. Thus, it seemed like only 2 components to pick from, and I figured the mobo was bad.

So I ordered a "new" A8N-SLI SE mobo from ebay. First thing I notice is that the mobo must not be actually new - I see some thermal paste on the white part of the CPU socket. Also, the CMOS battery came 100% dead according to my multimeter, which correctly reads a new CMOS battery @ 3.3V. Well, I decided to give it a shot anyway (with a new CMOS battery). Plugged in just the CPU (and cooler), outside the case. Flipping the PSU on, the mobo still needed me to jump the two "power on" prongs on the mobo to start it up, as expected. I did that, and to my joy I got a single beep out of the MOBO as it tried to post. Thinking it was odd that I didnt get more beeps (no memory, no VPU), I turned it off by cutting the power on the PSU. Started putting things back into the case, and before I got too far I tried firing it up again. Now when I flip the PSU on, the mobo comes right on w/o jumping the "power on" prongs b/c of the "restart on power failure" "feature" apparently. No big deal, except now its acting exactly like the other mobo. No beeps, no POST, power button will not turn the machine off. Pulled it all back out of the case, removed everything but the CPU to match my first test. Same thing - no beeps, no POST.

Is this a cut and dry case of "the CPU is bad"? Or am I missing something? I thought for sure, based on my tests of the first mobo, that the mobo was to blame. Now I'm not sure since the new mobo doesnt work either. However, the new mobo has me wondering, b/c I could tell that it was not actually 100% new, and the CMOS battery came 100% dead.

Adding to the variables here, I experienced something very very strange with the CMOS batteries. When testing the first mobo, one of the things I tried was replacing the CMOS battery with a new one, which I verified at 3.3v using a multimeter. Well, when I got the new mobo and noticed that the CMOS battery on that one was dead, I first pulled the new battery I put into the old mobo. Much to my chagrin, the battery was showing only 1.6V on my multimeter. So I purchased another new battery, and it showed at 3.3V as expected, so it's not a prob with the multimeter. So I put the new battery in the new mobo, and it was in there as I tried to get the new mobo to post/beep at me a few times. After each time where I turned on the PSU and fired up the mobo, when I pulled the battery out and retested it with my multimeter, the battery lost .02-.03V of charge. In just a few tests, it went from over 3.30 to under 3.20. So it's like when the mobo is running, my battery is being drained. What would cause that?

I'm just so confused/frustrated :(. I know this post is huge, but I wanted to answer as many questions as I could before they are asked. Any insight would be much appreciated.

Thanks!
-Brett
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#2
phillpower2

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:welcome: HitmanInWis

Can you borrow a known good PSU for testing purposes.

As a PSU puts out various voltages +3.3V, +5V and +12V it may appear that the PSU is working correctly but it is not, any significant drop of any output can prevent the system from booting up, the other scenario is a significant increase in the output which can be worse as it can fry one or more major components such as the MB, CPU, Ram, add on video card etc.

Please be aware that there are no user replaceable parts in a PSU so a bad one should be disposed of in a responsible manner and any type of conclusive testing will need to be done by a suitably trained Tech who has the required testing equipment and the relevant knowledge as to how to use it.
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#3
HitmanInWis

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I did attach the second mobo w/CPU and cooler only to a known good PSU as a final test, and I still got no beeps from the mobo indicating a tried (and failed) POST.

When I tested the existing mobo, I got consistent readings across all of the similar pins in the ATX connector and the molex/SATA connectors.

+3.3: 3.42v
+5: 5.28v
-5: -4.78v
+12: 11.97v
-12: -11.67v

I also tested the molex/SATA connectors with the mobo "running" and I did not see a significant difference.

Edited by HitmanInWis, 10 July 2012 - 05:59 AM.

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#4
phillpower2

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No beep = Power supply or system board problem.

Have you checked the power on button and the associated wires as what you described earlier;

Now when I flip the PSU on, the mobo comes right on w/o jumping the "power on" prongs


Suggests either a bad switch or damaged wire causing a short circuit in the case or MB.

FWIW you cannot do conclusive testing of a PSU with a multi-meter, techs use specialist testing equipment which simulates a PC under load which then causes the PSU to fail if it is faulty.

Any activity from the MBs onboard LEDs (see .jpeg 1)
Did you correctly connect the case connections to the header on the MB (see .jpeg 2)
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#5
HitmanInWis

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Most of my tests were run w/o any case wires (including the power button) connected to the mobo. The phenomenon of starting w/o jumping the power switch prongs happened on both motherboards, while both inside and outside the case. I was told that this is a BIOS feature, mostly meant for servers, so that if the mobo loses power (instead of a normal shutdown) it will start back up as soon as power is restored. Since my tests require me to turn off the system by cutting the power, I am triggering this feature.

As for LEDs on the mobo, for both mobos the Green LED is on while power is supplied, and the red LED is off.

Is there a good place to take the PSU for a free test? Or is this something generally paid for?
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#6
phillpower2

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Not sure where in the world you are so I can only suggest that you check the classified ads for local tech stores as there is more chance that they will have the correct testing equipment as opposed to a self employed tech who may not.

Some information regarding symptoms of a bad PSU http://www.aitechsol...chwtrblsht.html note the power good switch and +5V stand by details.
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#7
HitmanInWis

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I'm in the USA - specifically Wisconsin. I've taken PSUs to Best Buy to be tested in the past - they simply hook it up to some device and tell me in 2 seconds that "yep its good". If you think that their device is probably reliable, then I can probably do that.
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#8
phillpower2

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Never dealt with geek squad myself and so cannot speak from experience, what I can say is there is good and bad everywhere and if you look around google regarding geek squad you shall have your answer.

If you can use another tech service (some do test PSUs for free) and meanwhile let us know the present PSU brand and model name or number so that we can do some research.
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#9
HitmanInWis

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Wont be able to take a look at the computer for a few days. Will post back when I have more information.

Thanks!
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#10
phillpower2

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No worries reply when you are ready :thumbsup:
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#11
HitmanInWis

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Well...

I took the PSU into Best Buy today. While the dude had the tester on it, the PSU blew out a big puff of smoke sitting on the counter. Before that, the 4-pin CPU plug was only lighting up 1 of 2 lights. Thus, indeed it appears the PSU was junk.

So I bought a 600W Thermaltake PSU to replace the old 530W. I realize I dont just look at Watts, but this is a 7 yr old computer so it should be plenty.

Brought it home and tested with the two mobos AND now two CPUs (since I had ordered one before I made the initial post). Both mobos/CPUs acting with the exact same symptoms as above.
- No beeps
- No voice errors
- Auto-starts when power is restored (though with the new PSU there is sometimes a delay)
- CPU, Video, and Chipset fans all running.

Tries both MOBOs w/just CPU, and with CPU, Memory (1 of 2 sticks in 1 of 4 slots, switching for different tests), and Video card. I have the ATX power connected, the 4-pin CPU power connected, and the molex MOBO plug for the video card(s) connected. All nothing.

Wondering what I do next. Worried that perhaps the faulty PSU blew the first MOBO, and then when I tested the second MOBO with the old PSU it blew that one too. However, $80 for another MOBO off of ebay is an expensive guess and check that I've already done once. Any suggestions? Would it be a good idea to take the new PSU back to Best Buy and have them check it as well?
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#12
HitmanInWis

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Forgot to post. One thing I notice is that the ATX connector on the new PSU has one empty slot (only 23 wires). Looking up on the net, apparently that wire was removed from the ATX spec awhile ago. Is the A8N-SLI old enough to need that wire?
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#13
phillpower2

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You may have hit on something here as pin 20 is/was "optional" which means that it was required for some MBs to function but not for others, it may be required for the A8N-SLI as pin 20 is for the "Power OK" signal see table below;
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#14
HitmanInWis

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Found another 500W PSU I had laying around, with a 20-pin connector. Was pulled from a running computer, so it should still be in working shape. Tried both mobos, still nothing.

I really dont understand why with the new PSU it takes 5-15 seconds for the mobo to fire up after turning the power on, but that's beside the point I guess.

I think I'm going to chalk this up as a loss, and take everything in to a local technician. Called one up today and they said they will test both mobos/CPUs for me for $70 total, which seems reasonable. Hopefully they will test the memory, vid card, and PSU in the process.

Seems that by trying to save money, I've probably cost myself more - doh!
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#15
phillpower2

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Thanks for the update, sorry it is not better news though.
I hope that you are able to salvage something from this and please let us know how you get on with it.
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