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What points are corroded? What is the resistance to ground on PP3V42_G3H? Is PPVRTC_G3H present?

Bad ISL6259 and U4900. 12v went to the 3v data line of the SMC & ISL6259.

Quad bit is only for 820-00165/820-00163/820-4924/ 2015+ boards. 820-3023 is 2011, older, doesn't use quad SPI so no quad bit setting required. If you look at the difference in the SPI ROM in the schematic on the 820-3536 and the 820-4924 it should become easy to tell when quad SPI is needed and...

That's a dead PCH

and what were your findings with this?

remove the DC in fuse and apply 18.5v to the dc in fuse from an external power supply, then plug the magsafe in and tell me what behavior you get.

The resistors around U6100 are the first suspect. After that check CPU & MCP vcore. After that I would give the MCP a light heating and see what happens.

We cannot trouble any of the backlight boost circuit if it is not yet getting power. Q7706 is what supplies power to the backlight boost circuit, and it is outputting nothing. This must be dealt with before we touch the LED driver or anything else "after" Q7706. P channel mosfets here will...

does it happen when you tap on the ram slot?

What is the resistance between pins 17/18 on U7000 and pins 27/28 on U7000? Also are you putting load on the machine while it is charging?

3 AM is prime time for board repair!

Bad Q7080.

Idiocy on their part. Undo that! Is PP3V42_G3H present? Is CHGR_ACIN and CHGR_DCIN present? is SMC_BC_ACOK present?

Does it see the battery?

1) Voltage on pin 2 of U8070 for SSD_PWR_EN? 2) Voltage on pin 5 of U8070 for PP3V3_S0SW_SSD_FET? 3) What does L3700 look like? Measure in resistance? 4) What voltage do you get at pin 3 of U3740 for SSD_RESET_L, and pin 4 for SSD_RESET_CONN_L?

There must be something short circuiting once power is applied on PM_SLP_S3_BUF_L It can't be P1V5S0_EN/P5VS0_EN/P3V3S0_EN/P1V05S0_EN, or C8188/C8187/C8186 because they are all after other resistors. So cross those out. Pin 2 of R8178 connects directly to U3310 which is for thunderbolt. That's...

sandy bridge airs are the second worst behind the MCP79u airs. This is a case for the bin at this point.

Is a good and charged battery plugged in? Was there some film residue from liquid around the RAM or the CPU? Was the corrosion by the CPU mosfets? This is often fixed by an ultrasonic at 80c for a minute for me, dislodges the filmy junk around the RAM and under it that you cannot see.

usually bad L4600/L4700. Check diode mode measurement to ground, red probe on ground, on pins 6 & 7 of U4650 and pins 4/5/6/7 of U2760

What do you get in diode mode on the SDA and SCL lines to the ISL, red probe on ground, no power applied? Also check S4/S3/S0 rails for a short circuit. PPBUS_G3H will not come on if there is a short to ground for more than a few milliseconds.