Macbook Air A 2681 Board 820-02536 No turn on

[Sergio Kub]

Hello,
I have a Mac A2681 motherboard 820-02536. It was spilled in water. I had already cleaned it with isopropyl alcohol and managed to get it working. However, the keyboard, touchpad, and power button failed.
A month later, I replaced these components, and the motherboard no longer turns on.
F5200 resistance: 1 M Ohm
Stuck at 5V
Voltage doesn't pass the first transistor, Q5230
Can anyone help? I couldn't find the sequence.
I appreciate any tips or collaboration in advance.

[Sergio Kub]

C BMU SYS_DETECT NOTES
The BMU SYS_DETECT circuit relies on the system assembly in order to be properly enabled.
During assembly, a metal gasket is placed between the cowling and the top-side of the BMU flex.
The gasket is used to connect the BMU_CWL_DET_L signal, located between J5150.1 and Q5190.2,
to GND. Once BMU_CWL_DET_L is tied to GND, then the SYS_DETECT circuit is ready to be enabled.
The BMU VBAT output will be enabled after the BMU flex and cowling are installed and power is
supplied by connecting a power adapter to either the USB-C or MagSafe Connectors.
Thus the MLB remains in an unpowered state during system assembly.
Once the MLB is assembled into an enclosure, the BMU SYS_DETECT circuit output, SYS_DETECT_L,
is continuously sampled by the Gas Gauge IC at a rate of once per second until it detects a logic low.
During the once per second interval, an internal pull-up within the Gas Gauge IC is enabled for 4us to conserve
battery charge. Once a logic low is detected, then the BMU enables the VBAT outptu voltage.

[mon2]

F5200 resistance: 1 M Ohm

?? Power up and measure the voltage to ground on each side of F5200. Post the measurements. If this is the measurement across F5200 then the fuse is blown and needs to be replaced.

Without power to the board, measure the resistance to ground on each side of F5200. If the fuse is not blown, this measurement should be the same on each side.

[Sergio Kub]

Thanks for responding.
The fuse is not blown.
Without power to the board, the resistance measurement on the F5022 is high, around 1M Ohm.
The voltage does not pass through Q5230, right at the input.

[mon2]

Share the voltage to ground measurements of each pin on q5230:

source
gate
drain

[Sergio Kub]

It is a double transistor
First
Pin 3, 4 and 5 D - 5V
Pin 6 G - 0V
Pin 7 S - 0V
Consequently, the second transistor with all pins 0V,

[mon2]

Remove all power. Meter in resistance mode.

Measure the resistance across:

source & drain
source & gate
gate & drain

post each measurement.

[Sergio Kub]

S - D 700 K Ohm
S - G 350 K Ohm
G -D 6.37 M Ohm

[Sergio Kub]

Q5230 / 2
S - D 800K Ohm
S - G 700K Ohm
G - D 427K Ohm

[mon2]

The G-D measurement may be a bit low for the mosfet. Suggest to flux and remove this mosfet. Leave the mosfet off the board. Then power up again.

Does the first mosfet enable without this 2nd mosfet on the board?

[Sergio Kub]

Q5230 are 2 transistors in the same package. It's dual.
Should I remove the first one anyway?

[Sergio Kub]

There are two dual MOSFETs at the power input, Q5230 and Q5240.
The resistances measured were from the two MOSFETs in the first package. Q5230

[Sergio Kub]

I tested only with Q5230, without Q5240 and then swapped one with the other (they are the same). The Q5230 Gate is not activated by U5200. What signal would give the OK for the IC to activate the Q5230 input? It is not activating the MOSFET first because there may be something wrong ahead, like a short circuit.v

[Sergio Kub]

C BMU SYS_DETECT NOTES
The BMU SYS_DETECT circuit relies on the system assembly in order to be properly enabled.
During assembly, a metal gasket is placed between the cowling and the top-side of the BMU flex.
The gasket is used to connect the BMU_CWL_DET_L signal, located between J5150.1 and Q5190.2,
to GND. Once BMU_CWL_DET_L is tied to GND, then the SYS_DETECT circuit is ready to be enabled.
The BMU VBAT output will be enabled after the BMU flex and cowling are installed and power is
supplied by connecting a power adapter to either the USB-C or MagSafe Connectors.
Thus the MLB remains in an unpowered state during system assembly.
Once the MLB is assembled into an enclosure, the BMU SYS_DETECT circuit output, SYS_DETECT_L,
is continuously sampled by the Gas Gauge IC at a rate of once per second until it detects a logic low.
During the once per second interval, an internal pull-up within the Gas Gauge IC is enabled for 4us to conserve
battery charge. Once a logic low is detected, then the BMU enables the VBAT outptu voltage.

[Sergio Kub]

I think that's the problem, but I still don't know how to activate the battery.