Asus P4c800 Deluxe no POST

[nicolati]

Hi guys. I have a P4C800 Deluxe that doesn't execute POST.
I tell you the story:
1) One day the system didn't boot and the MB said "System Failed CPU Test".
2) I saw the solder glob under MB shorts with a PAD near it, under pressure of heatsink (known problem). I removed a few solder to eliminate the short. The MB didn't talk me anything yet. It's mute and doesn't POST.
3) The MB doesn't power on, if the CPU is not installed, only green LED.
4) I saw a SMD capacitor and a resistor near Power Switch partially burned. No any other caps (specially electrolitic ones) are damaged.
Any suggestion? Whatever kind of suggestion, please!
Thanks.
Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST

I add that a electrolitic capacitor is lightly up, but it doesn't seem damaged. I tested 3 voltage regulators with PSU on (green LED) but power off and all of them have a 0.00 V or a variable voltage. I don't know if I tested well; how are they testing ?
Bye
nicolati

[Gianni]

Re: Asus P4c800 Deluxe no POST

Can you post some pictures?

but power off and all of them have a 0.00 V or a variable voltage. I don't know if I tested well; how are they testing ?

What do you mean "power off"?
Variable voltage? You mean an unstable voltage?
If you can identify the regulators you can search the datasheet and after that you can check them or at least you can know what you should find on their pins.

Gianni

[nicolati]

Re: Asus P4c800 Deluxe no POST

Gianni, scrivo in italiano, che è meglio!
Intendo che non ho dato corrente alla mb, solo tensione (LED verde). Inoltre intendo che ai capi dei regolatori o c'è tensione instabile o non c'è ( 0 V ).
Solo che non so se ho misurato bene. Dovresti spiegarmi come misurare.
Grazie.
Ciao

[Gianni]

Re: Asus P4c800 Deluxe no POST

nicolati I know for you (and for me) it would be better to speak Italian... but this is not an Italian forum so please use English.
All members here can help you if they can understand what you are writing.
If I start writing in Italian it becomes "a restricted thread".

Now back to the problem.

Please post some pictures of your board, it would be easy to help you; try to take some close up of the damaged part.

About voltage regulators: I have here a dead Asus P4R800-VM but honestly I can't identify VRegs, I see a lot of DPAK PowerMos and 2 unidentifiable DPAK components.

Are you sure you have tested voltage regulators? Can you identify them by part number?
Only knowing what they are, you can check them: with the datasheet you can identify the input-output-ground pin, what is the expected output voltage... and so on.

Anyway if they are linear voltage regulators you must have the input voltage which is higher than the output voltage and one pin connected to ground or, if they are adjustable type, to a voltage divider connected between output-ground.

If I understand you the "green led" on the MOBO is ON but the PSU/CPU FAN are off; in this case you have only the +5VSt because you are in Standby mode so it is possible that you have no voltage on some parts of the board, VRegs included.

Solo che non so se ho misurato bene. Dovresti spiegarmi come misurare.

If you use a DMM (Digital Multi-Meter) it is easy to measure voltages, just place the pointed probes on the pins you want to measure; if you have a crocodile clips you can leave the GND ( - ) cable connected at ground and move only the positive( + ) probe on the point you want to measure. The cabinet is connected to ground.

If you don't post any pics, I think you won't get any useful help.

Gianni

[kc8adu]

Re: Asus P4c800 Deluxe no POST

pics can be the best way to help.
btw the adp3180 vrm chip tends to die on these.
fire it up and measure across the caps nearest the hsf.
is the voltage in the expected range?
some chips are marked and some set vcore by a set of pins on the cpu.
when the 3180 dies you get no vcore thus no post.

[nicolati]

Re: Asus P4c800 Deluxe no POST

Yeah, a 31...something is strange. I'll post photos soon.
I understand you Gianni, thanks for the reply.
Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST









Those are photos.
Any suggestion ?
Bye
nicolati

[Brian C]

Re: Asus P4c800 Deluxe no POST

2) I saw the solder glob under MB shorts with a PAD near it, under pressure of heatsink (known problem). I removed a few solder to eliminate the short. The MB didn't talk me anything yet. It's mute and doesn't POST.
nicolati

Is it the cpu BGA socket ? or the North Bridge BGA IC ?

[nicolati]

Re: Asus P4c800 Deluxe no POST

It was under a line of CPU.
Bye
nicolati

[kc8adu]

Re: Asus P4c800 Deluxe no POST

is that corrosion in that 3rd pic?
got wet while running?

[nicolati]

Re: Asus P4c800 Deluxe no POST

Yes, looks like a short, but I don't know how. The MB's owner is my friend. His case is a Silverstone and he has only Noctua fans, but he has a very very economic PSU.
Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST

The FET is marked 3310h...something and in some Russian forums they talk about that. If I test this FET badly, I can destroy sometihng else?
Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST

On that FET the voltage is stable at 1.91 V and it's cold.
Bye
nicolati

[Gianni]

Re: Asus P4c800 Deluxe no POST

Hi nicolati

you are right, the device 3310h its a PowerMos, I attach the datasheet.
You can test them with a DMM, here what I measure on the Asus MOBO:
between Gate-Source R greater than 6800ohm
between Gate-Drain R greater than 30000ohm
between Source-Drain R greater than 30000ohm
Take into account that values can change, they depend on where you place positive e negative probe, the value I wrote were the minimum I measured in both way.

If you use the DMM to check diode-junction, usually DMM has a diode "mode", you find around 470mV with positive probe on Drain and negative on Source; if you put the probe in the other way round you should have an open circuit. This 470mV is the body-diode junction always present in PowerMos.
These measurements tell you there the PowerMos are not shorted, but to really test them you should remove them from the board...
If you power up the MOBO you can measure the voltage on it: if the Gate is lower than -2.5V respect to Source, the PowerMos should be closed and you should have almost the same voltage on Drain-Source. If the voltage on the gate is between -2 and -1.7V, the PowerMos in working in linear mode so you should not found the same voltage ob Drain and Source, the voltage drop depends on the Drain-Source current. If the voltage on Gate is 0V or positive respect to Source, the PowerMos should be open and the voltage on Drain and Source must be very different. I tried to give you an explanation looking at the datasheet, I can't power the MOBO I have here.
Anyway it is hard to understand what it does without knowing the schematic; if it get hot, I mean you can keep your finger on it, it should be OK, if you burn your finger on it than something is wrong/damaged.

About VRegs the only one I see is 78L05A package is SO-8; it is a standard linear regulator and I suppose the input voltage is 12V while for sure the output is 5V, it is located near audio connector close to PCI slot.
Here you can find the datasheet.

The last unknown device i see is a Dpak with these mark: H J on top, second line 882, third line 4EA5.
I have no idea what it is.

I have no more suggestion even watching your pics, I am a newbie about MOBO problems, I am here like you to learn.

Gianni

[nicolati]

Re: Asus P4c800 Deluxe no POST

DS = 45 Kohm
GD = 48 Kohm
GS = 2.7 Kohm

Diode junction = 477 mV

There is a problem with GS resistance.

Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST

VDS = 0.09 V
VGS = 1.91 V
VGD = 1.8 V

This FET is broken, for me. It's always cold, even when the others are hot.

However, if I power on the MB WITHOUT the CPU, it should power on, isn't it ?
My MB doesn't.

Bye
nicolati

[nicolati]

Re: Asus P4c800 Deluxe no POST

The 78L05AC is input 12V and output 5V, as you said.
The other is H J 882 3DTA. There are two of these and one of H J 772 3ETB.
Bye
nicolati

[Gianni]

Re: Asus P4c800 Deluxe no POST

This FET is broken, for me. It's always cold, even when the others are hot.

If it is cold, it doesn't mean it is broken.

When you measured the Vgs, have you placed the negative probe on source and positive on gate? If the answer is "yes" than maybe it is broken but from the measure you made, it seems to me it is working.
Check it again (Vgs) and keep the negative probe on Source pin.
The voltage drop-out between D-S is 90mV, if we assume from datasheet an RDSon of 350mohm, the current is 257mA so the power dissipated is 23mW: the PowerMos can't get hot.

About the G-S resistor, 2.7Kohm is a reasonable value, I was worried if you have measured something less than 100ohm.

I have found the last device, I attach the datasheet. It is a NPN transistor.

Ciao
Gianni

[nicolati]

Re: Asus P4c800 Deluxe no POST

The HJ... I don't think is broken. I'll repeat tests. Does the MB power on without CPU ?
Bye
nicolati