After almost succeeding at repairing my mid-2012 Macbook Pro, I was back to square one. Not square zero as now at least I had some non-zero voltages on the board. The magsafe connector doesn’t turn on at all. My second suspect was the ISL6259AHRTZ that should be responsible for controlling the charger circuit and telling the MAX9940 to turn on. I found out the ISL6259 talks to the SMC through an I2C interface, so I plugged my logic analyser to the CLK and SDA pins to try to find out if they were talking. Turns out they were not, and the CLK line didn’t look like CLK at all. Time to replace the ISL.

The replacement was long and tiring, as it has tiny connections and tiny components all around it. At the first attempt, some lines that should not be shorted were shorted, so I had to start over, and ended up moving a few resistors/capacitors in the process. Took the opportunity to measure the resistors out of the circuit, and there was a resistor that was supposed to be 20Ω but was ~130Ω. Replaced this guy, powered it up and, nothing. Plugged my logic analyser to the I2C lines again and, ohh! Now the CLK line looks like a CLK signal, and I can even see what these guys are chatting about at the SDA line. What if I… tried to unplug and plug the magsafe a few times? Bingo! Sometimes it lights up green, then red after a second, and sometimes it doesn’t light up at all. Progress again, I guess? I also noticed that when I measure the SMC reset line with my multimeter, the magsafe goes green again for a few seconds. So I’d guess it’s the SMC that’s saying there’s something wrong to the magsafe… or the magsafe turns it red as it gets no answer? I don’t know yet… but the next step is to try to peek at the 1-Wire circuit. I’ll also buy some MAX9940 just in case.

Apparently these intermittent problems could be capacitors that are dying, so I’ll also check the capacitors for shorts. I think I’ll even replace the capacitors around these power circuits.