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Old 02-21-2020, 09:13 AM   #1
dicky96
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Default ASUS P6T SE powers on/off but will not POST

Hi guys now I have an ASUS P6T SE to try and fix

I would like to get this one working as I rather fancy putting a Xeon 3575 on it and making myself a really fast gaming PC on the cheap :-)

So the board powers on and off normally but does not POST. The POST card displays random numbers on power on - sometimes 00 but could be various others. Whatever number is displays remains static

From my little expecriance this usually shows the CPU is not running at all. On the POST card I have CLK and RST lit up RDY and FRAME do not illuminate

I'm using a known good i7-920 and DDR3 from another working board I have (different chipset unfortunately)

I had a look around, I have Vcore 1.15V to the CPU. What is bugging me is when I look on the capacitors on top of the Northbridge, I have one capacitor with 3.3V (orange on pic) and the others all have 1.12V apart from one (blue on pic) which has 0V across it and in fact it reads short circuit

I remember reading somewhere that a north bridge should have three voltage supplies so this would suggest I have a short on one of the supplies (either on the north bridge itself or elsewhere).

Problem is I don't know which supply rail is missing (what voltage it should be) and as I also don't know which end of the shorted cap is supposed to be ground anyway it's making it a bit hard to trace it.

it's an AC82X58 north bridge. I have the datasheet but that only seems to mention two supplies, Vcc and Vss

Anyone have a boardview, schematic, or any experience that would help me?

Cheers
Rich
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Old 02-22-2020, 07:51 AM   #2
SMDFlea
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Default Re: ASUS P6T SE powers on/off but will not POST

ive got the P6T 60-MIB870-B14 REV 1.01G boardview,not the SE.
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Old 02-22-2020, 08:30 AM   #3
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Default Re: ASUS P6T SE powers on/off but will not POST

Did you remove the processor and check the socket pins?

With your no-boot-but-can-power-off-and-power-on-normally-symptom, you possibly have a broken or bent pin.
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Old 02-22-2020, 09:17 AM   #4
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Default Re: ASUS P6T SE powers on/off but will not POST

Thanks, hopefully it will be very much the same. I don't know what is the difference between the P6T-SE and P6T-60

I've been thinking about this fault. There are several capacitors on the BGA which have 1.12V on them. The resistance to ground from these capacitors is about 6 ohms and the also fact there are several capacitors would suggest that most power is drawn from this supply. Could it be that Vcore to the CPU is the same supply rail, it reads practically the same voltage as Vcore?

The supply to the BGA which has 3.3V only has one capacitor and reads about 120 ohms to ground. I'm guessing that is possibly a Standby or Start Up voltage that may still be present when the ATX PSU is powered down? But I haven't checked to see if that is the case.

The missing voltage - would that be VTT? As I have seen on other boards that VTT does go to the north bridge. If I can't figure out where on the motherboard this voltage derives then I wouldn't know if the short has gone away if I removed the north bridge. I don't know enough about motherboard architecture (yet )

Last edited by dicky96; 02-22-2020 at 09:19 AM..
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Old 02-22-2020, 11:11 AM   #5
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Default Re: ASUS P6T SE powers on/off but will not POST

https://www.hardwaresecrets.com/unde...motherboard/4/

https://www.hardwaresecrets.com/unde...motherboard/5/

https://www.hardwaresecrets.com/unde...motherboard/6/

Interesting information. But it doesn't help me to understand what I want to know :-(

From that it seems I most likely have on my north bridge...

VTT (the 1.12V)
Something else... (the 3.3V)
And presumably something else again (the 0V) as it makes no sense to me to have a large capacitor, one end connected to ground and a short across it.

I remember now, I read some where that the third voltage supply was supposed to be for the graphics chipset (for north bridge with integrated graphics which I assume mine does not have). hmmm.

Last edited by dicky96; 02-22-2020 at 11:17 AM.. Reason: more info
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Old 02-22-2020, 11:18 AM   #6
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Default Re: ASUS P6T SE powers on/off but will not POST

Quote:
Originally Posted by RJARRRPCGP View Post
Did you remove the processor and check the socket pins?

With your no-boot-but-can-power-off-and-power-on-normally-symptom, you possibly have a broken or bent pin.
Sorry - missed that. Yes mate I did check all the pins under the microscope. They are fine and the CPU is known good.


-------------added

The board view looks like it may help me. I found the 1.1V and 3V supplies. There should also be a 1.5V IOH voltage and a 1.8V PLL voltage to the north bridge. Possibly the short capacitor is on one of those. Will have a look on Monday when back at the workshop

Last edited by dicky96; 02-22-2020 at 11:37 AM.. Reason: additional info
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Old 02-25-2020, 09:49 AM   #7
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Default Re: ASUS P6T SE powers on/off but will not POST

OK, although the board view is not for this exact version of the board, it is very very close to this motherboard I have

1.5V IOH and 1.8V PLL are present and correct. Neither go to that shorted cap on the BGA

3V on the bard view is actually 3.34V on my board but I am guessing that is actually OK

There are two voltages on the NB called VTTDDR and VTTXDP that the board view says 0.9V but I have 0.372V which seems wrong. The board view only shows those voltages on two pins of the north bridge and on a resistor pack so I don't know where they come from unless they are supposed to be some internal reference voltage generated in the north bridge?

H CPURST# is low (actually 0.108V) so the CPU is being held in reset

As the board view does not show the capacitors mounted on the NB I'm struggling to get further with this.

Unless some kind person has another motherboard with this X58 chipset and can check the resistance to ground from the capacitor on the NB BGA to ground for me (marked in blue on pics on post #1 of this thread) then i think I would have to get another working board myself to compare with this one. Or just assume the short on the NB cap is not a good thing (which I don't see how it could be to be honest) and change it anyway.

Last edited by dicky96; 02-25-2020 at 09:53 AM..
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Old 02-28-2020, 01:34 PM   #8
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Default Re: ASUS P6T SE powers on/off but will not POST

Hmmm , this board has alot of RAM slots , im no expert at repairing motherboards , but when i hear that computer is coming on , but no video , it suggests that the ram is bad... Have you checked the RAM power rails? there is a couple of mosfets probably close to the ram slot check to see if any caps there are shorted.
Have you tried different ram slots that may

If its not the ram, my suggestion would be to start taking things off , try to stay away from the NB chip because its a delicate thing and it can be fried easy with hot air... try to troubleshoot the mosfets next to the NB and caps , its ok if one of the mosfet pins is shorted to ground , but if they are both shorted then you have a bad mosfet.
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Old 02-28-2020, 01:36 PM   #9
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Default Re: ASUS P6T SE powers on/off but will not POST

Ofcourse it may not be the mosfet fault that you have the short , but once it is off the board you can check for sure.
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Old 02-29-2020, 03:45 AM   #10
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Default Re: ASUS P6T SE powers on/off but will not POST

I'm sure I checked Vram but I will double check

Normally if i board powers on and I have bad RAM (or no RAM) then it usually stops with C1 or C3 on my post diagnostic card. If three is no RAM it would also beep.

But this one doesn't. The POST card shows 0000, or some other random static number, which to me usually means the CPU didn't start running at all. The fact I can get other static number sometimes also makes me wonder if there is something wrong with the reset signal when I power the board on.

Also H CPURST# is low so I would assume that means the CPU is reset - it can't start.


Actually there is 0.108V on CPURST# and I am just wondering now as I type this if the North Bridge is trying to signal CPURST high but there is some low resistance (like a faulty MLCC cap) on CPURST so it can't go to 1V or whatever it should to start the CPU. When I'm back at the workshop I'll check the resistance from CPURST to ground.

On working board I would expect it to read high resistance or open circuit.

Also I could try force CPURST high to see what happens. Am I right to assume the signals logic high level would be basically the same as Vcore to the CPU/NB, or is it something else?

Hmmmm.....

Last edited by dicky96; 02-29-2020 at 03:48 AM..
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Old 02-29-2020, 02:53 PM   #11
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Default Re: ASUS P6T SE powers on/off but will not POST

dont assume anything lest u fry the nb and/or cpu with the wrong voltage. i know the intel datasheets have an absolute max voltage rating for the cpu powerlines, signal lines and PLL lines. so the proper way to find out the information u require would be to goto intel's site and download the relevant datasheets for the nb chipset family and cpu family u are working on.

pore through the datasheets. the voltage level to signal a logic high level for the cpurst signal line should be in the datasheet somewhere. use the find function in whatever pdf viewer u are using to find keywords relating to cpurst. that should help u.
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Old 03-17-2020, 12:28 PM   #12
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Default Re: ASUS P6T SE powers on/off but will not POST

Unfortunately this one is no more.

As no one advised otherwise I decided to change the north bridge but I desoldered the old one before ordering a replacement

However the profile I used (which has worked on several other north bridge) messed up this time. It managed to hit exactly the wrong temperature - enough to melt 95% of the balls but not quite enough to melt them in one corner. When the machine tried to lift the north bridge, it came away and then it dropped it because one corner was stuck

I modified the profile, not to use any higher temperatures but to shorten the soak by 20 seconds and increase the time for the last two ramp ups by 10 seconds and 15 seconds respectively. So the entire profile was 5 seconds longer but I got 25 seconds at the higher heat.

That did it and the north bridge came off cleanly but the first attempt had done the damage - about a dozen pads ripped off the board in the corner that had stuck

Interestingly enough after removal the short across the capacitor on the north bridge had gone. I was then able to determine which end should have been ground and which one not.

Then I soldered a short bit of wire directly to the cap on the north bridge, clipped my meter on that and then went around the BGA balls with the other probe until I could find where on the grid the cap was connected to. From that I could work out where it went on the PCB but there is no point tracing it now as the board is irretrevably buggered.

These profiles are a pain in the ass to get right, you think you have it on 10 boards then on the next one it bites you on the ass.

Nice try no cigar I guess.

Rich
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