HP - LA-D704P Rev 1.0 No Power Motherboard HELP

[harshana]

When I connect to my DC supply with 19.5v I see Unusual readings there like below.

Voltage: 19.5v which is OK.
Current: This one keep changing on every second. most of the time it is 0. (it take 0.00A,0.05A, 0.02A. Its rotating)

When I test Power section I noticed that the first mosfet take 19v but it doesn't out any. Reason is the gate voltage is equal to 0v.

I followed the sections and I noticed that something strange in Charging IC. Here are the values I noticed In my Charging IC.

Model: BQ24725A

Pin 20 (VCC) ----> 19v Seems OK
Pin 6 (AC_Detect) ---->2.59v Seems OK
Pin 12 (SRN) ------> 0.4v Seems OK

According to datasheet of this controller, above voltages are okay to out AC_OK and AC_Drive Signals. But It doesn't out them.

So I guess this IC needs to replace. But I would like to know your thoughts before I touch this IC.

Special: I noticed an Inductor which has low resistance which is 0.4ohms. I don't know what rail it is. But I will try to find out. I marked it on the image.

[mon2]

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

What is the voltage of charger pin # 4 (ACDRV) ?

[harshana]

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

What is the voltage of charger pin # 4 (ACDRV) ?

Both ACOK and ACDRV equal to 0v

[mon2]

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

Are you measuring these directly at the IC ?

What is the voltage of the REGN pin #16?

It will be a good idea to check the voltage on each pin on the charger IC so we can review against the datasheet.

[harshana]

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

Pin 16 also were 0v.

Im facing a power cut now. will send you the actual readings of other pins as well. I checked all the pins when I dig in to this. as I remember all the pins were 0v except the pins I mentioned above

[mon2]

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

confirm the Vcc pin of this charger IC - it must be powered for the REGN to function. The REGN must function to create the boosted GATE voltage required to enable the N-channel mosfets.

If the VCC pin is ok and receiving the power from the power adapter -> then remove all power. Meter in resistance mode -> check the resistance to ground of the REGN pin.

Is the REGN pin being loaded down ?

Also good to check the resistance of the DCIN mosfets to see if they are shorted or not.

Hints are towards this charger IC being defective since the REGN pin is not showing the ~6 volts.

[harshana]

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

confirm the Vcc pin of this charger IC - it must be powered for the REGN to function. The REGN must function to create the boosted GATE voltage required to enable the N-channel mosfets.

If the VCC pin is ok and receiving the power from the power adapter -> then remove all power. Meter in resistance mode -> check the resistance to ground of the REGN pin.

Is the REGN pin being loaded down ?

Also good to check the resistance of the DCIN mosfets to see if they are shorted or not.

Hints are towards this charger IC being defective since the REGN pin is not showing the ~6 volts.

pin 16 ———-> 96.3kohms

My fault. I just checked voltage in pin 16 and I see 6.14v there.

DCIN mosfets are not shorted

yes I test directly from the IC pins.

[harshana]

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

Here are the actual Voltages of the Controller.

Pin 1,2,3,5,7,8,9,10,14,15 ------> 0v
Pin 4 -------> change between 0v and 0.2v (I see its trying to get a value. but not stable.)
Pin 6 -------> 2.59v
Pin 11 ------> 0.27v
Pin 12,13,18 ------> 0.42v
Pin 16 ------>6.14v
Pin 17 -----> 5.91v
Pin 19 ------> 0.17v
Pin 20 ------> 18.90v

[mon2]

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

Remove the series resistor that is between ACDRV (Pin #4) and the target mosfets.

Then check the voltage on ACDRV (Pin # 4) again.

[harshana]

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

Remove the series resistor that is between ACDRV (Pin #4) and the target mosfets.

Then check the voltage on ACDRV (Pin # 4) again.

Now its value is 0.07v

[mon2]

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

Post the voltages on the DCIN mosfets.

Remove all power -> post the resistance values of the mosfets as well.

[harshana]

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

Post the voltages on the DCIN mosfets.

Remove all power -> post the resistance values of the mosfets as well.

1st Mosfet

Pin 1,2,3,4 ------> 0v
Pin 5,6,7,8 -------------> 19.26v

Drain to Source ----> 9.02kohms
Drain to Gate -----> No value
Drain to Ground ------> 0.48Mega ohms
Source to Gate ----> No value
Source to Ground -----> 0.54Mega ohms
Gate to Ground ----> No value even in 20M range

2nd Mosfet

all pins have 0v

Drain to Source ----> 73.1kohms
Drain to Gate -----> No value
Drain to Ground ------> 1ohm
Source to Gate ----> No value
Source to Ground -----> 4.14kohms
Gate to Ground ----> No value

[mon2]

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

Drain to Ground ------> 1ohm

Remove the 2nd mosfet and check if ACDRV returns to an expected value.

[harshana]

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

Remove the 2nd mosfet and check if ACDRV returns to an expected value.

Now It returns 1v

[harshana]

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

Also I soldered the resistor back and now I see the 1st mosfet is okay. he pass 19v

[mon2]

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

ok. Concern is with the 2nd mosfet and also why the main rail is showing 1 ohm to ground.

That is not good news and may again be a CPU fault.

Without the 2nd mosfet (which is now likely to be defective and must be replaced) -> what is the resistance to ground of the main power rail (drain of the 2nd mosfet) ?

Maybe, perhaps maybe, you have a bad cap on this line but again could be a bad CPU.

Confirm pins 5-6-7-8 of PQB2 resistance to ground.

(while I fix my clothes dryer from h*ll - the 3600W heater element fell out of its notches and was heating up the back wall of the dryer - almost burnt my hands - now we know why it took ~4 hours to dry the clothes. The fixture was supposed to heat up the dryer cabin - not the back wall nor burn my hands)

[harshana]

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

ok. Concern is with the 2nd mosfet and also why the main rail is showing 1 ohm to ground.

That is not good news and may again be a CPU fault.

Without the 2nd mosfet (which is now likely to be defective and must be replaced) -> what is the resistance to ground of the main power rail (drain of the 2nd mosfet) ?

Maybe, perhaps maybe, you have a bad cap on this line but again could be a bad CPU.

Confirm pins 5-6-7-8 of PQB2 resistance to ground.

(while I fix my clothes dryer from h*ll - the 3600W heater element fell out of its notches and was heating up the back wall of the dryer - almost burnt my hands - now we know why it took ~4 hours to dry the clothes. The fixture was supposed to heat up the dryer cabin - not the back wall nor burn my hands)

Still 1ohms.

[mon2]

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

With a power supply -> dial up 1 volt (or even 0v8) @ 3A or whatever you can.

Inject this voltage onto the drain pins of the removed mosfet so that you can feed onto the main power rail.

Who is heating up? Similar to your last case. With some luck, some capacitor will do the heating which means the capacitor is defective / shorted.

Otherwise, if the CPU, then the CPU is defective.

On this laptop, is the CPU removable? Guessing not and is soldered.

[harshana]

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

CPU isn’t removable. anyway will this cause to damage cpu if cpu rail defective?

[mon2]

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).