Diagnostics point to bad SMC on faulty macbook board. I gotta pull one off of scrap board, remove solder balls from it, reball it. Gonna need a good flux and a good solder paste.
I lay down a sheet of copper for a work surface. Double-sticky tape mount the pulled chip bottom-up. apply and tape down reballing stencil with kapton (polyamide) tape. flood with liquid flux, schmear solder paste into stencil holes, slowly pre-heat copper sheet, move-in hot air rework nozzle (400C, 39lpm airflow) – slow and careful watch heat effect the built-in flux in the solder paste…work it around evenly, slowly…melting the solder into balls:
It took me trying different nozzles, lower and lower air flow rates until I had to upgrade my hot air rework station to get the low air flow + high thermal capacity mix that would not burn out the heating element – I had to learn the hard way to use a high-temp drying tacky LIQUID flux and use solder paste instead of pre-sized balls. My first efforts had solder balls blowing around, melting together in other stencil holes – this job must be done only one specific way for good results and not too much headaches / frustration. (I’m still learning and trying to master this skill. This procedure works best for me right now.)
GREAT job! Now, to pull up stencil and clean the chip.
ooh. I waited too long! The flux is no longer at temperature and has formed a glue bond! Apply 100-150C while prying…
The balls look good. But I used a Q-Tip and 99%IPA to clean off flux. Q-Tip left hairs. Pesky cleaning job I’ve made for myself.
All clean and ready to place on board!
Not so nice just YET! The other side – under inspection – showed a couple balls not making proper contact to pads. I reflowed SMC and tapped it down a couple times lightly while solder balls were wet, causing all balls to bond SMC contacts to board pads. I replaced TPS51980 U7501 that generates 5v, 3v rails for SMC_PM_G2_EN and fan ran, magsafe lit up, everything was perfect.
Or so, it seemed!
Of course, that’s not all this board was up to. I put the board into Macbook chassis, all happy and proud of myself. Ready to call the customer with the news of victory. The USB Bluetooth multiplexer IC was trolling. Board had 1 second fan spin, reset, 1 second fanspin, reset, etc. Intermittent PM-SLP_S4_L. I had noted that PP5V_S4_RS3 was intermittent. But I just replaced SMC and U7501! What, you mean I’m gonna have to THINK here? No way! Form of: THERMAL CAMERA! Lazy hack: ACTIVATE! A small chip, USB3740 U3510 was glowing then going cold, glowing, then going cold. Pull the offender! Plug board in: IT RUNS! Now, check traces where that USB BT MUX chip came from for short to ground: none! GOOD! Scrap board had a spare part for me. Well we just put that on our customer’s board so they can have Bluetooth action. Now the board is testing 100% so far. Revived from it’s grave.
The culprits in this caper sit awaiting their timeout.
This repair was originally a liquid damage fix. It ran fine and then came back two days after 90 day warranty. I fought and FOUGHT with this thing. I learned it a lesson, but good. Sometimes liquid damage doesn’t show until much later. That’s why I warranty my work for 90 days.
SUCCESS! (This is the first time I ever diagnosed bad SMC, reballed another SMC, soldered it to the board and realized a fix from doing so. It’s a good feeling. Bad SMC is usually something you don’t accept, you don’t want to believe it – you refuse to bite the bullet and do this job – mainly because low confidence of results, questionable state of replacement pulled part, etc.)