MBP 13" Power issue/ Voltage drops

[Lu Kim]

Hi everybody. First time posting but have been reading the forums for a long time. I have an A1278 with the 820-2879-B Logic board with a power issue. It will not power up with the Magsafe plugged in or off the battery. When the Magsafe is plugged in I get the bright green light on the adapter. I have tried the SMC bypass, but had no luck. I have checked G3HOT curcuit and I get 3.4v. The issue i'm having is pin 5 on the Mosfet located at Q7085 all the way to the fuse located at F7040 the voltage jumps up and down. On pin 5 of Q7085 the voltage will start out at 18.5v but will start to drop all the way down to 2.5v and back to 18.5v. On both sides of the fuse located at F7040 the voltage will start at 12v then drop to 2.5v and back to 12v. It continues to do this until you unplug the Magsafe.