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Old 07-02-2018, 03:07 PM   #1
slayernn
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Default Asus P8Z68 troubleshoting

Hi all, this is my first post and im not new to forum What i like on this forum is that many advanced/pro users know real causes and never try to assume that symptoms of fault is in user, for eg : "did you try to plug power chord" and similar idiot "im trying to be smart" assumption we all see on many of well known forums.
Let me go straight to the topic:
I got Asus P8Z68 deluxe mobo which sudenly stop working (according to past owner), when PSU is plugged in, power button glow red and reset green, when i press pwr button, nothing happend, only thing that happen (except this onboard leds) is that northbridge is geting hot so i assume that problem is with NB chip/power lines to it, as NB shouldnt be warming when pc is off.
I tried to short green-black psu lines while sitting on mobo and then it start (fan spin, red lights showing problem with cpu,memory,pci-e) for like ~20 seconds before shutdown. Another thing to mention Q-led is not turning on. Another thing to say, i tried every posible scenario (with/without mem,vga, 12v cpu rails, checking 1155 pins, reset bios etc) and nothing happend, power button is always red,no fan spining,northbridge is getting hot.
Is problem in northbridge? What to check and which vrm belongs to NB, its maybe faulty mosfet,cap or so, related to it? One more thing to say, many capacitors on mobo looks like little bent and not sitting properly on surface, is it posible that some of them failed even they are polymer caps? Any advices will help me troubleshoot this mobo, thanx in advance!
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Last edited by slayernn; 07-02-2018 at 03:21 PM..
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Old 07-05-2018, 10:00 AM   #2
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Default Re: Asus P8Z68 troubleshoting

Not northbridge, i mean southbridge*! My fault.
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Old 07-06-2018, 05:57 AM   #3
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Default Re: Asus P8Z68 troubleshoting

Let's call it the PCH using the official Intel naming to avoid the mistake (but yeah in reality it's a southbridge)
Does the PCH get hot while the board is completely off? (ie. power button wasn't pressed, PSU fan not spinning)
With your multimeter in resistance mode, measure the resistance across the ceramic capacitors directly onto the PCH package. Write down the various values you can measure (doesn't matter which capacitor it is).
I may have the boardview for this motherboard, I will check that later.
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Old 07-06-2018, 09:00 AM   #4
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Default Re: Asus P8Z68 troubleshoting

Quote:
Originally Posted by piernov View Post
Let's call it the PCH using the official Intel naming to avoid the mistake (but yeah in reality it's a southbridge)
Does the PCH get hot while the board is completely off? (ie. power button wasn't pressed, PSU fan not spinning)
With your multimeter in resistance mode, measure the resistance across the ceramic capacitors directly onto the PCH package. Write down the various values you can measure (doesn't matter which capacitor it is).
I may have the boardview for this motherboard, I will check that later.
Thank you for your answer. Yes PCH is getting hot while board is completely off, power button wasn't pressed (onboard pwr button glow red and couldnt start board anyway). I tested for cap resistance, pic is uploaded. Do i need to test something while board is connected to PSU? Thank you for your effort! Best regards.
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Old 07-06-2018, 02:42 PM   #5
piernov
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Default Re: Asus P8Z68 troubleshoting

Yep, the PCH is shorted. 0.2 ohm is a full short to ground and since the PCH itself is heating up, he is the culprit. Sadly this can go to the trash bin.
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Old 07-06-2018, 02:58 PM   #6
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Default Re: Asus P8Z68 troubleshoting

I do agree that the PCH/SB shouldn't be getting very warm when the board is off. But nevertheless, how do you define that "hot"? Burning hot(i.e. can't keep your finger on it)? Or just warm?

Sounds like most likely either whatever regulator is providing power to the PCH/SB is either bad or the PCH/SB is bad itself. Normally, most motherboards have at least one regulator that converts the 5VSB rail from the PSU to 3.3V, and this 3.3V rail is always present on the motherboard (sometimes there are also regulators for 1.8V and/or 1.5V too, depending on what's required.)

My suggestion is to take one multimeter probe and put it in the 24-pin ATX connector on pin 5VSB (with the PSU disconnected from the motherboard, of course). Then, with the multimeter set to lowest resistance scale, find all regulators and MOSFETs on the lower half of the board that have less than 2-3 Ohms resistance to 5VSB. Report what you find here. One of these should be for the PCH/SB. Or if you'd like to wait for Piernov to upload the boardview instead to find that regulator, that's fine too. This is just an alternative way of finding things when you don't have schematics or boardviews.
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Old 07-06-2018, 03:11 PM   #7
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Default Re: Asus P8Z68 troubleshoting

Quote:
Originally Posted by piernov View Post
Yep, the PCH is shorted. 0.2 ohm is a full short to ground and since the PCH itself is heating up, he is the culprit. Sadly this can go to the trash bin.
Damn :/ hate when there is no way to fix, but thats lottery when buying cheap Thanx man!
@momaka yep, burning hot to touch. I belive piernov is right and there is no way to fix ;\ thx

Last edited by slayernn; 07-06-2018 at 03:14 PM..
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Old 07-06-2018, 03:19 PM   #8
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Default Re: Asus P8Z68 troubleshoting

Yeah, most likely it is. Though I've also seen once instance where a shorted ceramic cap caused the regulator behind it to pulse On and Off, and thus overheat other components connected on the line.

But easiest way to know... and since the board is dead anyways - remove (unsolder) the PCH from the board and see if you still get 0.2 Ohms on the ceramic caps on top of it. Of course, I don't know if this would be worth your time. But maybe you're trying to learn how to do BGA work (i.e. remove BGA chips and etc.), it might be.

Other than that... yeah board is probably headed for the trash (Though I suggest keeping it for useful parts if you do repairs regularly - the MOSFETs and some of their PWM controllers/drivers can be valuable when fixing other stuff).

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Old 07-06-2018, 03:41 PM   #9
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Default Re: Asus P8Z68 troubleshoting

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Originally Posted by momaka View Post
Yeah, most likely it is. Though I've also seen once instance where a shorted ceramic cap caused the regulator behind it to pulse On and Off, and thus overheat other components connected on the line.

But easiest way to know... and since the board is dead anyways - remove (unsolder) the PCH from the board and see if you still get 0.2 Ohms on the ceramic caps on top of it. Of course, I don't know if this would be worth your time. But maybe you're trying to learn how to do BGA work (i.e. remove BGA chips and etc.), it might be.

Other than that... yeah board is probably headed for the trash (Though I suggest keeping it for useful parts if you do repairs regularly - the MOSFETs and some of their PWM controllers/drivers can be valuable when fixing other stuff).
Good sugestion. Now what i did is take off PCH (with heat gun), first time do that Apart that i by mistake lost 2 small caps (and right now i found them on table), other caps show ~50 ohms, so i asume PCH chip is ok? Anyway it would be hard to put it back now Ths
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Old 07-06-2018, 04:26 PM   #10
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Default Re: Asus P8Z68 troubleshoting

Well, if the 0.2 Ohm caps now read ~50 Ohms... yeah, PCH might be okay.

Putting it back on IS possible, but you will need new 1.0 mm solder balls, or whatever size the original ones were (fairly cheap on eBay, AliExpress, and etc.) First clean the board and PCH from old solder, though - for this, you'll need a more powerful iron, like 50 Watts minimum (more if it's regular wall-type). Then use it to roughly "collect" all of the solder from the board and PCH (use lots of flux - it will make things easier). Then do one more pass with lots of flux and desoldering braid. Once the board and PCH pads are cleaned (pads on board and PCH should feel pretty smooth), you can proceed to put the new solder balls on the PCH/SB. Now this is the hard/annoying part, especially if you don't have a stencil, as you would literally have to move every solder ball into place by hand (or rather very fine tweezers). I've done it before, but it's pretty precision work. And I felt like my eyeballs were going to fall off afterwards from all the strain .
...Then re-melt the solder balls on the PCH with hot air (but not heat gun, as that is too powerful and will likely blow away the solder balls). Then put chip on board, align, and re-heat again to attach it to board.

All of this is not too hard, but certainly time consuming - especially if doing it for the first few times. And you will need lots of PATIENCE.

That aside, before attaching the chip to the board (if you even intend to do that repair ), first we should check where that 0.2 Ohm resistance is coming from that is causing the PCH to overheat.

Last edited by momaka; 07-06-2018 at 04:31 PM..
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Old 07-07-2018, 04:44 AM   #11
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Default Re: Asus P8Z68 troubleshoting

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Originally Posted by momaka View Post
Well, if the 0.2 Ohm caps now read ~50 Ohms... yeah, PCH might be okay.

Putting it back on IS possible, but you will need new 1.0 mm solder balls, or whatever size the original ones were (fairly cheap on eBay, AliExpress, and etc.) First clean the board and PCH from old solder, though - for this, you'll need a more powerful iron, like 50 Watts minimum (more if it's regular wall-type). Then use it to roughly "collect" all of the solder from the board and PCH (use lots of flux - it will make things easier). Then do one more pass with lots of flux and desoldering braid. Once the board and PCH pads are cleaned (pads on board and PCH should feel pretty smooth), you can proceed to put the new solder balls on the PCH/SB. Now this is the hard/annoying part, especially if you don't have a stencil, as you would literally have to move every solder ball into place by hand (or rather very fine tweezers). I've done it before, but it's pretty precision work. And I felt like my eyeballs were going to fall off afterwards from all the strain .
...Then re-melt the solder balls on the PCH with hot air (but not heat gun, as that is too powerful and will likely blow away the solder balls). Then put chip on board, align, and re-heat again to attach it to board.

All of this is not too hard, but certainly time consuming - especially if doing it for the first few times. And you will need lots of PATIENCE.

That aside, before attaching the chip to the board (if you even intend to do that repair ), first we should check where that 0.2 Ohm resistance is coming from that is causing the PCH to overheat.
Hehehe man, your entusiasm rox! Respect It would be hard for me to do this way, timeeee consuming and still, if i put chip back to board properly, i still have to solve problem from beggining and I dont have enough knowledge for that, only ears/eyes for suggestion on what to check/fix. Thnx for explenations and steps for mazohistic balls replacing! ;}}}
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Old 07-08-2018, 06:57 AM   #12
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Default Re: Asus P8Z68 troubleshoting

If the caps were really measuring 0.2ohms and the PCH was heating up while the board was off, I'm not sure what else it could be than a dead PCH.
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Old 07-08-2018, 04:57 PM   #13
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Default Re: Asus P8Z68 troubleshoting

Does it do this without a CPU installed?
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Old 07-08-2018, 09:47 PM   #14
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Default Re: Asus P8Z68 troubleshoting

Quote:
Originally Posted by piernov View Post
If the caps were really measuring 0.2ohms and the PCH was heating up while the board was off, I'm not sure what else it could be than a dead PCH.
Depending on what kind of regulator is feeding the PCH in standby, that could be the source of the problem too. I've seen 1117 and 78xx regulators go short-circuit between all three pins. Since one of those 3 pins is often ground on these (save for the adjustable 1117), you could possibly end up with a very low resistance to ground across whatever device that regulator is powering.

While this is a rare occurrence, I still check for it.

Quote:
Originally Posted by brethin View Post
Does it do this without a CPU installed?
Good point to check that.
Possible that something wrong with the CPU or CPU socket could also cause troubles, as some of the PCH pins are directly tied to that.

Last edited by momaka; 07-08-2018 at 09:48 PM..
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Old 07-09-2018, 07:30 PM   #15
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Default Re: Asus P8Z68 troubleshoting

Dead 1117 is a thing indeed, dead Ethernet controllers too, and in this case they can send some power lines that the PCH uses too to ground. But the PCH won't get hot. if the PCH is getting hot with a 0.2ohms short to ground, it's him. PCH resistance on its VCore is somewhere around 10 to 100 ohms usually. On the 3VSB line it's in the kohms range.
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