HP - LA-D704P Rev 1.0 No Power Motherboard HELP

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Yes if the voltage is too high. This is the reason to keep the voltage down to the minimum so that if there is a leak to the CPU rail, you are only at the safe boundaries of the CPU.

The CPU voltage is often 1v05 or lower but 1v05 is ok.

Personally, use 0v8 but have a 10-20A voltage injector from Sunshine or some brand like that. If you want, can share the full details tomorrow when at the office.

It works well to locate shorted caps. For CPU, often you need to remove the heatsink so you can feel if the CPU is the shorted component.

So what 'may' have happened is that some buck regulator (takes in the high voltage like 19vdc) and supplies a low voltage (like perhaps the Vcore rail @ 1v05) will have external mosfets. External mosfets are used to dissipate heavy currents like the Intel / AMD CPUs which are pigs on current. They can consume hefty current in normal operation.

If the high side mosfet leaks, then the high voltage leaks through to the CPU and kills it.

For such a case, it is too late to repair this unit unless you have a BGA rework station and time. Good BGA stations are very $$. We have a very high end one and it is more expensive than my car. Works very well to remove and replace parts, even larger BGA devices or down to 0.5*0.5mm components. Fully automatic.

Respectively, it is not possible to remove and replace with a standard hot air gun due to the size of the CPU / PCH in a single package. At the very least, underside heating table is required (which is integral to our BGA station).

It takes 1.2A and I can feel a capacitor heating up.

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Finally Identified the bad guy. It was the mosfet near to the cap. Im not sure 5v or 3v because schematics aren’t totally match

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

I soldered 2nd mosfet back and I see its working fine now. however I can’t see 3v or 5v from the board.

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Very nice!! Good job!

I can't see 3v or 5v from the board.

Which part is not working ? Can you link the part # ?

Are you referencing the following are not working ?

+5VALWP
+3VALWP

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Very nice!! Good job!



Which part is not working ? Can you link the part # ?

one mosfet which is from 3v/5v rail.

however Now Im facing another problem.

I didn't saw 3/5v from the chip. when I look closely I saw that the chip isn't soldered correctly.

Its my friend's laptop and he told me that he took this laptop into a shop and he failed to fix.

when I soldered it correctly Now that chip also heating up (3v/5v controller)

I checked its pins and I noticed that the pin 9 has short to ground.

lets continue fixing this

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Now that chip also heating up (3v/5v controller)

Is it PU301 ?

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Is it PU301 ?

according to schematics yes it is.

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

With care, measure the voltage on each pin of PU301. If you believe the part is getting too hot then it is likely defective and needs to be replaced. This is common and have seen it before where this part fails.

This part is supplying multiple rails including:

a) low current LDO rail - pin 14 = 5v0; pin 13 = 3v3. Are these present ?

If not, check their resistance to ground but again, remove all power first.

b) switch power supply rails which are heavier currents so there are external mosfets used to take on the heavy loads @ PQ301 and PQ302.

Are these rails both off ?

If yes, remove all power and check the resistance to ground of the following:

+5VALWP
+3VALWP

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

With care, measure the voltage on each pin of PU301. If you believe the part is getting too hot then it is likely defective and needs to be replaced. This is common and have seen it before where this part fails.

This part is supplying multiple rails including:

a) low current LDO rail - pin 14 = 5v0; pin 13 = 3v3. Are these present ?

If not, check their resistance to ground but again, remove all power first.

b) switch power supply rails which are heavier currents so there are external mosfets used to take on the heavy loads @ PQ301 and PQ302.

Are these rails both off ?

If yes, remove all power and check the resistance to ground of the following:

+5VALWP
+3VALWP

I was able to compare schematics with the board and as I can see I have removed PQ301. which is from 3v section.


Here what I found.

Now the chip returns 5v from pin14 but get heat. I guess its because pin 9 grounded which shouldn't.

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

No. This device has numerous rails.

Pin # 9 = switching regulator rail for 3v3 and works with PQ301. This leg has nothing to do with the LDO rail.

The LDO rails are always low current rails that are intended to supply 500mA (educated guess or lower). They simply 'burn' the high voltage of 19v down to 5v0 or 3v3, etc.

It is quite normal for this IC to be warm if the 5v is working since it is burning down the 19v input to the lower 5v level.

What about the LDO leg of 3v3 @ pin # 15 ? Is that leg working ?

Again, this has nothing to do with the legs with the coils / inductors.

PS: Just wolfed down (too) spicy sambar & idli. Wife's cooking is getting better

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

No. This device has numerous rails.

Pin # 9 = switching regulator rail for 3v3 and works with PQ301. This leg has nothing to do with the LDO rail.

The LDO rails are always low current rails that are intended to supply 500mA (educated guess or lower). They simply 'burn' the high voltage of 19v down to 5v0 or 3v3, etc.

It is quite normal for this IC to be warm if the 5v is working since it is burning down the 19v input to the lower 5v level.

What about the LDO leg of 3v3 @ pin # 15 ? Is that leg working ?

Again, this has nothing to do with the legs with the coils / inductors.

PS: Just wolfed down (too) spicy sambar & idli. Wife's cooking is getting better

I powerd the board around 30 seconds to test 3v pin. he had 0.6v and now both arent present. I guess PU301 died now. he heated a lot

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

No. This device has numerous rails.

Pin # 9 = switching regulator rail for 3v3 and works with PQ301. This leg has nothing to do with the LDO rail.

I saw that pin 9 directly connected with 3v inductor

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Ok. Sounds like it. Remove this part and make a note of the pin #1 location for the replacement.

After the part is removed -> with no power -> check the resistance to ground of the 5v LDO pin # 14.

Then check the resistance to ground of the LDO pin #15.

Then do the same for the coils @ PL302 (for the switch 3v3 rail) & @ PL303 (for the switching 5 volt rail).

It is important to know that each of these legs should not be too low in resistance. Confirm it.

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Pin 14 -----> no value
Pin 15 ------> 4.3ohms

PL302----> 0.4ohms
PL303 ---->66.6ohms

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Ouch. These are low values again (except for pin 14).

As per before, dial up your power supply to 1 volt + 3A-5A only.

Inject the voltage @ PL302 coil. Who is heating up ? (hope it is not the CPU).
Inject the voltage @ PL303 coil. Who is heating up ? (hope it is not the CPU).

Inject the voltage @ Pin 15. Who is heating up ? (hope it is not the CPU).

For each injection, keep the voltage to low as possible (0v8 to 1v0 is ok).

Ideally you will find bad caps again.

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

No one is heating up or doesn’t feel to my finger tips. injected 0.8v with 5A

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

Hmm. Not even the CPU ? The resistance sounds quite low on the rails but now you can try to solder this back and/or replace it.

Given that another shop already worked on this board, perhaps it was not soldered on properly ?

Aliexpress will have these parts (as usual).

Also suggest to inspect the 2 x mosfets on this regulator to confirm they are not damaged. With the power off - check their resistance as usual:

source & drain
source & gate
gate & drain

When you go shopping, order a few spares of these & DCIN mosfets - just in case.

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

power supply says that the circuit take around 4.8A. so how could this happen??? how they stay without heating ��?

[mon2]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

My thoughts...the CPU which is under a heatsink may be heating up but cannot be detected.

Do check the mosfets on this regulator if you are injecting the 'ALWP' rails. Are they heating up ?

Do note that each of these devices is a DUAL MOSFET inside a single package. So the HIGH and LOW side mosfets are inside the PQ301 & PQ302 devices. Perhaps they are shorted internally ?

Check with your meter but observe which pin is which for the resistance checks.

[harshana]

Re: HP - LA-D704P Rev 1.0 No Power Motherboard HELP

I removed the heat sink to confirm the cpu condition. so we can ignore it. and also yes I focused on mosfets as well. checked the removed mosfet and noticed it has the short. so we can confirm its dead. however the strangest part is impossible to have that kind of low resistance as I know. Anyway again power cut. I will continue in the morning