ASUS ASUS P5VDC-MX Dead CPU?

[socketa]

Hi y'all,

Good PSU/voltages
CPU fan spins continuously - but no POST/Beeps
Tried several good RAM in all slots
Power LED on "system panel connector" does not light up - get 1.4V across terminals
Green SB light is activated on Mobo
Shuts down when holding in power button
12V present on input caps, but no voltage on CPU caps (2 X 6.3v lytics and 5 X 4v smaller metallic "FL" caps)
Removed CMOS battery and replaced.
Also tried starting with no CMOS battery - But no change in situation

If the CPU is faulty, does that mean that the VRM controller may not be activated?

[RJARRRPCGP]

Re: ASUS ASUS P5VDC-MX Dead CPU?

CPU fan spins continuously - but no POST/Beeps

Socket pins are the first thing to suspect on socket 775. Especially when it still powers up.
If it powers up, then it's possible that it's just bent or a broken socket pin that's not shorting.

(Only if the socket is fine, could RAM slots then be a possibility.)

IOW, it's usually socket pins followed by RAM slots.

Only if socket pins look fine would I then check the VRM circuit...

But, I see that the motherboard in the photo has the heatsink on, thus the CPU got to be in there, too, so that makes the likelihood of a bad socket pin lower...

It honestly looks like a bad socket pin, VRM problem or a broken trace to the CPU.

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

can you burn your finger on the via chip or the small heatsink?

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

some serious heat was here!

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

All of the pins look good
Replaced with known good CPU, but still no change

The backside of board (that you circled green), and the the cap on the opposite side of the heatsink, shows no signs of heat damage.

No, the VIA chip, or the north bridge HS, does not get hot
After 5min:
NB = 18 deg c
SB = 20 deg c
Ambient temp = 17.5 deg c

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

what is the 3pin thing that got hot?
maybe it's now dead.

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

What 3-pin thing are you referring to?

Also, there is Power getting to the USB Ports (5.23V) as soon as the power button is pressed.
Furthermore, the potential difference across the Power LED pins on the "system panel connector" is 1.44V - which is not enough voltage to light up the LED.

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

3pin package in the circle, the heat that darkened the board came from it's legs!

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

That's a vacant capacitor location.
Looking at the reverse side of the board, it doesn't look like there was any cap there to start of with - looks factory soldered
I did an image search for this board, and all the photos that i looked at showed the position to be unoccupied.

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

not the missing cap, the fet/regulator just below it.

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Is that what happens when a mosfet fails - it seriously overheats?
Is the sink leg (as opposed to the gate) the one that would heat up like that, as there is no evidence of overheating anywhere else around the mosfet

And what would you do next?

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Here is the voltages across all the mosfet legs when it is turned on
I've labelled all the mosfets A to O on the photo
Letter Gate Drain Source
A 0 0 0
B 0 0 0
C 0 12.4 0
D 0 12.4 0
E 0 12.4 0
F 0 0 0
G 0 0 0
H 2.75 3.37 2.75
I 2.1 3.4 5.2
J 2.17 3.43 5.0
K 3.08 2.46 1.63
L 3.9 3.38 2.46
M 12.4 5.2 5.2
N 5.7 2.6 0
O (hidden behind RAM) 7.99 5.2 2.7

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

still waiting for a part number.

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

The mosfet in the green circle is: Advanced Power Electronics Corp AP9T15GH

I get multimeter readings of:
1.53V G-S
2.12V D-S

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Also noticed that the CMOS battery was dead.
Replacing it made no difference
Am only getting 0.17V across CMOS terminals

[momaka]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Looks like either CPU is not being detected by the board or the board gets stuck before even POST begins. Or perhaps CPU VRM controller is dead or not getting a signal from the board to start running the CPU (but that would be a very rare case).

Try this: remove the RAM and see if the board beeps at you (usually two beeps).
Also, see how much resistance you get between Drain and Source on MOSFET H. Make sure to keep the multimeter on it for at least a few seconds (if there are any caps, they may need a moment to charge, and then your readings will settle more)

.

And just for your information:
C, D, and E are upper MOSFETs of CPU VRM
A, B, F, and G are lower MOSFETs of CPU VRM

MOSFET M is a pass-through MOSFET (when the PC is on), likely for RAM VRM supply
N is lower MOSFET of VRM for RAM Vdd (2.5 Volts for DDR, 1.8 Volts for DDR2)
O is upper MOSFET of VRM for RAM Vdd (2.5 Volts for DDR, 1.8 Volts for DDR2)

MOSFET L is likely for Northbridge<->RAM communication (2.5 V for DDR and 1.8V for DDR2... I think)

MOSFET K is either 1.5 Volts for the AGP connector or RAM Vtt and NB<->RAM communication (normally, that's should be about 1.3V, though, so probably AGP)

MOSFET J converts 5 VSB power into 3.3 V standby-power for the SouthBridge

MOSFET H... I have no clue! 2.75 Volts seems a bit too high for Northbridge Vcc (which tends to be 1.6 Volts or less for boards from that era). Yet, it is very close to the NB, which suggests NB Vcc supply. Or

The SOT-223 component labeled "I" on your diagram is perhaps for the clock generator - that "ICS" chip with crystal next to it. And possibly for the RealTec audio and LAN chips.

So overall, most of the voltages seem fine, except for CPU VRM, which is just not there.

I have an ASUS A8V-MX, which is the socket 939-equivalent of your board... more or less. At least it appears to have the same Via NB/SB combo and same AGP and PCI-1x slots. I'll try to pull it later this week and see if I get similar voltages to yours.

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Thanks for the additional info

Removed RAM - No difference

There is a RT9245A chip (Multi-Phase PWM Controller for CPU Core Power Supply) just under the Heatsink and after power button is pressed it has 5V on Vcc pin - So power is getting to the VRM controller

[momaka]

Re: ASUS ASUS P5VDC-MX Dead CPU?

Check pin 9 (PGOOD) to see if the controller is getting a Power Good signal.

[socketa]

Re: ASUS ASUS P5VDC-MX Dead CPU?

I'm assuming that you mean pin 10 (not pin 9) of the RT9245A chip.
Got no voltage on this pin after power button is pressed

Also checked:
Pin 27 (PWM1) = 0V
Pin 26 (PWM2) = 0V
Pin 25 (PWM3) = 0V
Pin 24 (PWM4) = 5.2V

[stj]

Re: ASUS ASUS P5VDC-MX Dead CPU?

i think those via chips should be running hotter - check they are getting power.

i'm still thinking about that cooked fet.
maybe it's blown or something it's powering is shorted.
it really isnt normal to see that kind of heat mark.