MacBook - 2021 A2485 - 16 inch - 820-02100-A - No Boot / No Power

[applejuice95]

If you're asking me to stick one lead on the top of 667 and the other lead on the top of 707.. Theres anywhere from 5M Ohms to 7K Ohms of resistance. Jumps all over the place

[applejuice95]

You saw the message about L5800 glowing under thermal when power is plugged in right? Via MagSafe or USB-C either way. ??

[applejuice95]

..

[mon2]

Then there is a trace break between CR707 and CR667 (and equivalent). At your discretion, mate a piece of wire to create a common power rail, which it is not at this time.

As an example, use a piece of wire to join CR667 to CR707 (or similar). Be 100% sure the netname is the same on the source and destination of the wire. Most likely the liquid damage and ultrasonic bath ate away at the trace(s) that mated these on the PCB.

[applejuice95]

There is no component on the board that these two meet at?

[applejuice95]

Sorry, I'm an idiot..

Was reading the ground side of the damn caps CR667 637 and 607.

Resistance to ground all the way around for this rail is 2.5K Ohms

[applejuice95]

How can we test Inductor L5800? Since its glowing under thermal when board has power?

[mon2]

I have not seen this board on my bench so you are my eyes.

Are there parts @ UR700? UR730? UR600? UR630? UR660? If yes, check what the resistance is from this region's PP3V8_AON to L5800.


** IGNORE the above - not relevant **

Why is L5800 heating up and powering off? Someone is consuming too much current and exceeding the current draw and forcing this regulator to power OFF. Then the cycle repeats.

Study who consumes this power rail. Test the resistance to ground on each such rail and you will find your bad boy (not Will Smith).

Hunt for the CPU rail and check it first.

[applejuice95]

Just for giggles heres a photo of it..

Hard to measure this because the Inductor is on the other side of the board.

BUT - this measurement of Res to Ground, is a whopping 1-0.8 ohms across all of those parts

[mon2]

Ok - this is literally a dead short. To confirm, you are measuring the resistance from L5800 to ground and the resistance is ~1R = 1 ohms?

Next, repeat but with one probe at L5800 and the other probe @ PPVDD_DCS_S1. What is the resistance?

Internally inside the U7700 device are mosfets that take the higher voltage of PP3V8_AON and lower it to the required CPU voltage. If the mosfet has leaked, the target low voltage device is likely to be dead and then it is game over.

Do you have an adjustable power supply? You can use that power supply to dial up 0v8 to max of 1v0 and inject this voltage onto the shorted PP3V8_AON rail. Then test which part on the part heats up. If it is the CPU, game over. You will have to remove the heatsink to observe if it is heating up.

[applejuice95]

No L5800 to ground is 4.5K Ohms both sides..

You asked to measure L5800 resistance to UR600/700 regions PP3V8_AON local rail (which by the way is CR667 , CR607, CR637 orCR737, CR767, CR707)

That measurement is .8 Ohms.. Nothing there..

UPDATE - Resistance of L5800 to PPVDD_DCS_S1 is 3K Ohms

[mon2]

Aside from L5800, someone else must be heating up. Search around with your thermal camera. Someone is consuming this heavy current and causing LF5800 to heat up.

[applejuice95]

R6809 gets hot first then goes down before L5800 heats up. How do you test resistors like this to see if they are good or not?

Thank you for all of your help.

[mon2]

Unable to find R6809.

[applejuice95]

R5809 - My apologies.

When I plug power into board: And look under thermal

R5809 flashes for a second, then Q5800 flashes for just a second, then L5800 starts glowing steady ..

As fast as 123.. Very fast.. flash, flash, steady glow.

Should I inject voltage on this 3V8 rail that includes both this glowing inductor and the resistor?

[applejuice95]

Voltages of Q5800 pins

Pin 1 - 12V

Pin 3 - 3.8V

Pin 4 - 0.8V

Pin 5 - 3.8V

Pin 6 & 7 - 3.8V

C5811 coming from pin 4 has 9V on pin 1 and 3.8V on pin 2

Voltage on L5800 is 3.8V on both sides

[mon2]

Do you see the same on Q5820 and Q5840? Also thermally throbbing?

[applejuice95]

Only L5800 glows. Q5800 glows for less than a second when the computer cycles.

U2000 gets some glow.

and UG900 flashes for less than a second every 8 seconds or so.

[mon2]

Remove all power. Measure the resistance across the capacitor @ C5810. What is the measurement?

[applejuice95]

Found a short at CN983. Put it back together. Got it to get to DFU finally. Restored OS.

Machine so far works. but has no backlight. And when HDMI is plugged in, the screen is fuzzy. So no external display, and no internal backlight. Cannot confirm if the display assembly is bad or not, very odd that external display gives white fuzzy screen and no display