Chosen Solution
Spilled coffee on the upper keyboard/fan outlet. Wiped off and left powered on (I now know that was stupid)— after a couple minutes one string of LEDs turned off, followed by the other. The display still works (can test with torch behind apple logo) and it can still drive an external monitor. Board number is 820-3787-A. I have had a good look at the logic board and nothing obvious—main fuse is okay, LCD connector seems okay, WLED driver is okay and supplying correct voltage.
I have a .brd of the board and have checked some other components. This chip Q7706 appears to be the culprit. From the schematic it looks like pins 6, 5, 2, 1 should have 12.6V when pins 3 and 4 supply 12.6V. I am getting 0v on 6, 5, 2, 1. Would it be reasonable to assume that the chip is dead or is it more likely a short somewhere else?
Also I notice that the capacitor C7701 on my board is missing, shown in upper left of the yellow circle. Could this be a difference in board schematic or could it have burnt off? Would appreciate some help before I continue any further. Thanks!
Looks like you’re on the right track! Do you have access to the needed parts as well as have micro-soldering skills?
