HP Probook 640 G5 - replaced blown components, getting power led, fan full, 5-flashes on CAPS Lock and NUM lock, black screen

[zlr8r]

Hey guys, bit stumped with this laptop after replacing 2 blown components i.e., MP86493, MP2979A.

To begin with, this laptop was dead-dead.

Now with replaced (visibly) blown components, i do get some progress; after connecting battery or main cable;

• am getting white power led
• 5-long-flashes on CAPS Lock and NUM lock
• then, fan full speed
• CPU heats up some (smaller die PCH, does not)
• always constant black screen no matter what's tried
• no USB recognition
• no HDMI output

this is as far as I can get with it and not sure where to inspect next ?

I tried to emergency flashback the Bios but its not recognising USB. Also tried various RAM sticks.

There is no 'heat' at all from the smaller die (PCH?) on the CPU chip ? Even the coils to it are cold, but voltage is there at the coils/mosfets.

There are no shorts on the board as far as i can tell... also tried injecting 1V, 2A at cold coils and nothing heats up on thermal camera?

Grateful for any guidance/pointers on what to test/check next ? cheers


Burned Chips replaced;

MP86943 MP2979A

[zlr8r]

....anyone?

[zlr8r]

can anyone offer advice ? thanks

[piernov]

Usually CPU is dead as a result of a VRM IC/high-side MOSFET short.

[zlr8r]

Usually CPU is dead as a result of a VRM IC/high-side MOSFET short.

Thanks for info.

I do seem to be getting all necessary voltages to make the board work.

In thermal view, I see just 3 inductors heating up along with the cpu.

The rest of the board is ice cold.... including the small die on the CPU. it almost seems like there is no power getting to the smaller die ?
If that was the case, what would cause that and where on the board can i check to verify ?

If the CPU was dead as you say, would it power up at all ? How can i test this ?

If i repeat power connection connecting the battery, the battery does appear to charge. But thats all this board does (see video).

I've included a thermal pic below alongside it in normal view. Also a Video showing the boards voltage and amps draw once the power is connected.
(note: i dont need to press the power button for it to start up, it does this itself. I can turn off the board using its button normally.




The video is taken from the moment i plug in the power connector (without battery)

[zlr8r]

...anyone

[siddiq]

9 times out of 10 the CPU dies as a result of VRM IC/high-side MOSFET shorts like piernov said .... I've read in other forums where members in similar situations had to replace the CPU to fix the motherboard.... you can checkout google for working voltage coil resistances for your CPU....

[mon2]

The CPU power rail is created by the switching of multiple mosfets that take turns (phases) turning on/off so that not one leg is over worked. If either of these legs gets damaged, then the high side mosfet of ~19v can leak onto the CPU power rail which expected ~1v or under. A single transient can cause this fault to kill the CPU. Test the resistance to ground at these inductors that are heating up. No power to the board during these tests. The other power rails that are working are not relevant to this one since they are independent legs of the circuit. The battery can also continue to charge under these conditions. The CPU rail may not be able to power up because of the short condition of a damaged CPU. The current sense circuit is sensing a higher than normal load here and shutting it down and may be operating in a 'chirp mode' -> cycling between ON / OFF cycles to prevent additional damage to the power supply rails.

[zlr8r]

The CPU power rail is created by the switching of multiple mosfets that take turns (phases) turning on/off so that not one leg is over worked. If either of these legs gets damaged, then the high side mosfet of ~19v can leak onto the CPU power rail which expected ~1v or under. A single transient can cause this fault to kill the CPU. Test the resistance to ground at these inductors that are heating up. No power to the board during these tests. The other power rails that are working are not relevant to this one since they are independent legs of the circuit. The battery can also continue to charge under these conditions. The CPU rail may not be able to power up because of the short condition of a damaged CPU. The current sense circuit is sensing a higher than normal load here and shutting it down and may be operating in a 'chirp mode' -> cycling between ON / OFF cycles to prevent additional damage to the power supply rails.

thankyou for that great information... I am still learning.

as original post states, there are no 'obvious' shorts on the board unless the low value i do get at the cpu inductors, but i thought that was to be expected anyway ? (like, 1-3 ohms?)
Ill post results of checking resistance to GND . If i inject 1v to the CPU coil, will that indicate a blown CPU on thermal camera?

again many thanks