820-00164 no power when flex cable to Left IO board connected

[brispy5]

Hi Everyone.

I am new to this forum and am excited to be a member.
I am an experienced troubleshooter who is terribly rusty at board level diagnosis and repair. I have most of the necessary equipment: ultrasonic cleaner, AmScope microscope, hot air station, hakko fx-951, quality fluke meter, power supply, etc.

I have a macbook air 11" MLB 820-00164 that I am using as a training board.
It has no liquid contact of any kind.
Did not power or have any magsafe light when I received it.
Troubleshot and repaired the one wire circuit (thanks Louis!) at and around U7090 (a couple dodgy traces and bad resistor). Magsafe adapter now lights up, but machine does not power UNLESS the flex cable from left IO board is disconnected. Machine will boot all the way to login.

Further troubleshooting found a bad Q3080 not passing PPVIN_S4SW_TBTBST_FET to pin 27 of U3090.
This may have been a lucky find as this circuit seem to be for Thunderbolt.

NOW: When flex cable is connected the voltage at cathode side of D3095 is 0V
When disconnected it is 15V
I am still getting familiar with the process and in understanding the various power states and how to determine this.
Any and all guidance would be greatly appreciated.

 

[Alan.L]

have you try take the I/O board out to check for signs of liquid ingress? also have you try another I/O board and flex cable?

 

[Alan.L]

When the board doesn't boot with I/O board flex cable plugged in, what are the voltages on pp3v42_g3h and ppbus_g3h?

 

[brispy5]

sorry for the delay, I've had a terrible cold. The left IO is new as is the flex cable. I'm using them as diagnostic parts. please stand by for the results for checking pp3v42_g3h and ppbus_g3h . . tomorrow if I am better....

 

[brispy5]

ppbus_g3h = 8.591 V measured at r7006 pin 1

pp3v42_g3h = 3.397V at c7098 pin 1

 

[dukefawks]

Are you using the correct IO board and cable for 2013+ models? Picture of connected board+cable+motherboard?

 

[larossmann]

I get at least 3 machines a month from stores plugging the dc in flex upside down so this is my first thought.

 

[brispy5]

No Title

all parts are from the customer's machine. I'm pretty sure....

 

[brispy5]

Sorry if it takes me time to respond. I sometimes don't have the time....

 

[dukefawks]

That IO board is definitely not new, I can see corroded test points in the picture already.

 

[brispy5]

I might have mis spoke about the IO board. My bad. I can't recall to be honest.