HP16 DAG3MMB3AAO REV A No power on, no led charger

[judamex]

I have an HP 16 DAG3MMB3AAO REV A. The charge LED doesn't turn on.
So far, I've checked the three input MOSFETs, and all three seem to be in perfect condition. The charge IC is a BQ24781. The voltages I've checked are:
VCC: 19V
REGN: 6V
ACDET: 2.45
ACOK: 2.85

It's striking that I don't have voltages on the ACP, ACN, and CMSRC.
I'm a bit stuck on how this controller works and why it won't turn on.

[mon2]

Reference:
https://www.youtube.com/watch?v=L2eu...thraLaptopCare

What is the voltage to ground of ACDRV?

Remove all power. Meter in resistance mode. Measure the resistance to ground of ACP. Then the resistance to ground of ACN.

Finally, measure the resistance between the pins ACP and ACN. Do so with the meter probes directly on the ACP and ACN pins. We are interested in the full path resistance of these 2 pins. Post each measurement.

If you have a schematic, post the link to the schematic but only share the schematic inside the sub-forum for schematics.

[mcplslg123]

Since CMSRC is missing,ACDRV has to be low only. ACDRV goes high only when you have ACDET/ACOK and CMSRC present.

How you checked the DC-IN mosfets? Please share the readings in resistance mode between
01.Drain-Source
02.Drain -gate
03.Source-Gate

[Sephir0th]

And the share model of the DC-IN Mosfets when they are fine. Absolute possible that these are NOT controlled by the charging controller if they are P-Channel.

[judamex]

I am guided by the following schematic diagram


These are the mosfets on the input line

[judamex]

Since CMSRC is missing,ACDRV has to be low only. ACDRV goes high only when you have ACDET/ACOK and CMSRC present.

How you checked the DC-IN mosfets? Please share the readings in resistance mode between
01.Drain-Source
02.Drain -gate
03.Source-Gate

Mosfet 1 diode mode
Drain (R) - Source (B)= .OL
Drain(R) Gate(B)=.OL
Source (R) Gate(B)=0.592

Mosfet 2 diode mode
Drain (R) - Source (B)= .OL
Drain(R) Gate(B)=.OL
Source (R) Gate(B)=0.592

Mosfet 3 diode mode
Drain (R) - Source (B)= 1.8
Drain(R) Gate(B)=.OL
Source (R) Gate(B)=0.590

[judamex]

Reference:
https://www.youtube.com/watch?v=L2eu...thraLaptopCare

What is the voltage to ground of ACDRV?

Remove all power. Meter in resistance mode. Measure the resistance to ground of ACP. Then the resistance to ground of ACN.

Finally, measure the resistance between the pins ACP and ACN. Do so with the meter probes directly on the ACP and ACN pins. We are interested in the full path resistance of these 2 pins. Post each measurement.

If you have a schematic, post the link to the schematic but only share the schematic inside the sub-forum for schematics.

ACDRV (pin4) its on = 0.010V
Resistence between pin APC and ACD is 0.9 ohm

[mon2]

Resistence between pin APC and ACD is 0.9 ohm

Between ACP & ACN?

What is the resistance to ground of ACN?

[judamex]

Between ACP & ACN?

What is the resistance to ground of ACN?

yep, between ACP(pin1) & ACN(pin2) = 0.9ohm
resistance for ACN(Red) to GND(Black) =15.45k

[mon2]

Using the lowest resistance scale on your meter, touch the probes together. What is the resistance?

[judamex]

Using the lowest resistance scale on your meter, touch the probes together. What is the resistance?

Touching the 2 probes, this is the reading I got on the lowest measurement my multimeter has.

This is the reading by touching ACN(Pin 1) ACP (pin 2)

[mon2]

Measure each leg of the pcb traces. Measure ACP pin to the entry of the current sense resistor. It should 0R ohms. Repeat with ACN to the other side of the same resistor. Should be 0R ohms again. We are assuming the posted partial schematic is the same as your board.

[judamex]

Measure each leg of the pcb traces. Measure ACP pin to the entry of the current sense resistor. It should 0R ohms. Repeat with ACN to the other side of the same resistor. Should be 0R ohms again. We are assuming the posted partial schematic is the same as your board.

the resistance between ACN (Pin1) and the sensing resistor (PR8200) is 0.6 as is ACP (Pin2) with (PR8200) is 0.6

[Sephir0th]

ACDET is barely on the border of showing a acceptable voltage (2.4V min.) So maybe worth to take a look here and see what happens when higher voltage (2.6V - 2.7V) reaches this pin.

Other than that the BQ24781 are known for notorious failing. So I guess the "Brute-force" method, so simply to replace it would be a option here. Iirc it is interchangeable with BQ24780S.

[judamex]

ACDET is barely on the border of showing a acceptable voltage (2.4V min.) So maybe worth to take a look here and see what happens when higher voltage (2.6V - 2.7V) reaches this pin.

Other than that the BQ24781 are known for notorious failing. So I guess the "Brute-force" method, so simply to replace it would be a option here. Iirc it is interchangeable with BQ24780S.

I replaced it with a BQ24780S and the conditions remain exactly the same. How could I increase the AC voltage? It's currently 2.49. Could I remove or change the value of any resistors?

[mon2]

Yes.

1) Review the calculator here:

https://learn.sparkfun.com/tutorials...e-dividers/all

2) Use 19v as input and the resistor values onboard your logic board.

Use this video as guidance:

https://youtu.be/L2eurrCKT2k?t=327

3) Based on the video and shown typical resistor values, the ACDET should be ~2v59. Locate the resistors on pin # 6 (ACDET) of the charger IC.

4) Carefully flux and remove the resistors to measure their resistance. Compare the values to the YT video. To raise the voltage, use a lower resistance value for the low side (the resistor that is going to ground) resistor. Be sure to stuff the next resistor value into the above calculator to understand the expected voltage. Do not power up without the resistors in place and be sure the final voltage is within spec for this charger IC (use the public datasheet for the BQ24780S to understand this specific charger IC).

[judamex]

Yes.

1) Review the calculator here:

https://learn.sparkfun.com/tutorials...e-dividers/all

2) Use 19v as input and the resistor values onboard your logic board.

Use this video as guidance:

https://youtu.be/L2eurrCKT2k?t=327

3) Based on the video and shown typical resistor values, the ACDET should be ~2v59. Locate the resistors on pin # 6 (ACDET) of the charger IC.

4) Carefully flux and remove the resistors to measure their resistance. Compare the values to the YT video. To raise the voltage, use a lower resistance value for the low side (the resistor that is going to ground) resistor. Be sure to stuff the next resistor value into the above calculator to understand the expected voltage. Do not power up without the resistors in place and be sure the final voltage is within spec for this charger IC (use the public datasheet for the BQ24780S to understand this specific charger IC).

I changed both resistors to 470k and 75k respectively, obtaining 2.56V in ACDET, but the result is the same, neither the charging LED lights up, nor is there any change.

[judamex]

I changed them again, now I put the first resistor as 430k and the second with 75k, getting 2.71V but still nothing happens, there is no LED and there is no ACDRV, nor ACP or ACN

[mon2]

Ok.

what is the resistance to ground on ACN pin? No power to the board while testing resistance or diode mode.

what is the voltage to ground of:

acok
regn
vcc
cmsrc

on the charger ic?

[judamex]

Ok.

what is the resistance to ground on ACN pin? No power to the board while testing resistance or diode mode.

what is the voltage to ground of:

acok
regn
vcc
cmsrc

on the charger ic?

The resistance between "acn" and GND: 15.5K.

The voltage at the following points is:
acok: 2.88V
regn: 6.07V
vcc: 19.32V
cmsrc: 0.015V
acdet: 2.7v