Notes on Magsafe 3: 
Only the Magsafe 3 cable that comes with the 140W USB-C charger will work with it, the Magsafe 3 cables from the 14" M1 and M2 Macbook pro and M2 Macbook Air will NOT work/charge and will make the Magsafe 3 head blink orange.
Lower wattage USB-C chargers that come with Magsafe 3 have been untested as of yet.
The 140W charger and the Magsafe 3 that came with that charger will charge any Magsafe 3 macbooks normally.
If the magsafe 3 head blinks orange and its the original that came with the charger, then try cleaning the Magsafe 3 port with a microfiber towel and some isopropanol. (Feel free to correct this info if you discover something new)
The 140W charger can be used normally with a regular USB-C charging cable, up to 96W with macbooks as well as with any USB-C charged device.
Magsafe 1 and 2:
Magsafe 1 and 2 work identical. The only difference is in the mechanical shape of the plug. Magsafe-2 is longer and narrower than Magsafe-1.
1. Test a known good DC-IN board first, and make sure you have a genuine MagSafe cable. Newer machines are extremely fussy about being able to communicate with the charger tip properly.
2. Check PP3V42_G3H is 3.42v. Without this G3 rail the SMC will remain unpowered, along with other important circuits, i.e.: 1-Wire.
3. Check SMC_RESET_L is high. If this signal is missing then SYS_ONEWIRE will not come up to communicate as the SMC is stuck in reset mode; SMC is in RESET when signal is L(OW).
3a. Check the SMC is powered (Can be checked at the PP3V3_S5_SMC_VDDA inductor).
3b. Check the SMC is running (PPBUS_G3H gets boosted by roughly 400mv, varies per model).
4. Check the service port for corrosion as PP3V42_G3H and SMC_RESET_L both show up here.
5. Check the 1-Wire circuit is working as it should (If it's on the logic board, MacBook Air have 1-Wire on the LIO board, which should already be ruled out in step 1).
5a. On MacBook Air 3437/00165 boards, make SURE to check R7012 is not damaged and measures 68k regardless of whether you have PP3V42_G3H, or not. Sometimes you can be led to a dead end, and this resistor is the culprit of all your misery.
6. Remove the MAX9940 IC to check ADAPTER_SENSE and SYS_ONEWIRE voltages. Both sides should be chattering at around +3v through the MAX9940, this IC is there to stop 14.85+ volts going to the SYS_ONEWIRE bi-directional data line and cooking the SMC.
6a. If both are at the correct voltage check C7000 and R7029, replace MAX9940 if necessary.
6b. If ADAPTER_SENSE is low check the ADAPTER_SENSE line back to the DC-IN board.
6c. If SYS_ONEWIRE is low you most certainly have a faulty SMC. This line comes directly from the SMC straight to the MAX9940 (In most cases?).
· SMC_BC_ACOK must be present on both pins 2 and 3 (A+B) of the U7001 AND gate otherwise it will not open and let 3.42v out to create SMC_BC_ACOK_VCC.
· If the capacitor (C7000) on SMC_BC_ACOK_VCC goes bad then current will go directly to ground as it will become the path of least resistance; therefore, U7000 won’t be powered.
· Sometimes adapter voltage can leak onto ADAPTER_SENSE. This will cause U7000 to trigger overvoltage protection and shut off to protect the SMC.
· Just because a MacBook turns on, it does not rule out the System Management Controller. One way to tell if the SMC has a bad SYS_ONEWIRE line is as follows: Plug in a charged battery, power on the device and start MacOS, then plug in the charger and see if the light comes up after 10-60 seconds and MacOS detects charging. If so, this indicates a partially faulty SMC.
· In RARE occurrences you may get away with flashing the System Management Controller.
· On a MacBook Air, it’s always a good idea to check J9500 and the LIO Board Flat Flex Connector. Corrosion can damage either of them and affect communication across SYS_ONEWIRE.
· PP3V42_G3H can be pulled low by corrosion hidden in, or underneath the keyboard connector.
· Fake MagSafe chargers will work when a battery is plugged in, however usually fail to charge the device once the battery is flat or unplugged, they also FORCE voltage into the system. Put fake chargers where they belong 🗑️. When in doubt use a CMIzapper MagSafe Tester to see if the charger is real or fake.
· Sometimes PP3V3_S5_AVREF_SMC (and other SMC circuits) can become shorted to SMC analogue ground; this will cause strange and temperamental behaviour, including no light on the charger.