Thank you all very much for your answers!
Tough question. You can try analysing some laptops schematics (Google that) to try to understand how they work. Besides that, a strong knowledge on digital and analog electronics and patience (lots of it). You can also look for individual components datasheets to get to know what they do, how they are powered, what kind of signal(s) it needs to do its job, etc.
I googled and found the schematics for my model. It is an Apple MacBook Unibody A1342 (K87):
http://schemalaptop.blogspot.de/2013/03/apple-macbook-a1342-mlb-k87-macbook.htmlI will attach the schematics here too.
Your best bet is to ask on the macrumors forums.Ive recently fixed an A1278 with water damage,though nowhere near as bad as yours.
http://forums.macrumors.com/showthread.php?t=972699
Youll also find various schematics there .Good luck with it .
EDIT: Clean up the board with isopropyl alcohol and a brush and see how bad it looks .The hardest part will be identifying all the parts that need replacing.Make a decision,try and repair it or salvage as many parts as possible to sell on,namely the HDD,memory,dvd , keyboard, and the logic board even in its present state would sell.
I bought isopropyl alcohol on Amazon:
http://www.amazon.de/gp/product/B001FSXLMU/ref=oh_details_o00_s00_i00?ie=UTF8&psc=1I poured a bit IPA on the pcb and cleaned it with an electric toothbrush.
The result does not satisfy me. Dust is still sticking on the pcb and components and the fluid left some lines on the surface behind. Maybe I have to repeat the process more times or pure more IPA on the pcb.
For now, I will keep the parts. If I fail repairing the macbook, I will try to sell them.
you need isopropylic alcool (IPA), a toothbrush or an ultrasonic bath (or both)
you spray the ipa on the corroded parts, then brush with energy and rince again with ipa
then a bath some minutes with ipa under ultrasonic pulses
you let it dry some hours
and you try to power on
sometimes you have to start this over 2 or 3 times, depends if you have some "alive" signs or not.
the display is dead you must buy another part but for the logic board it's not totally lost IMHO
good luck.
I will try to repeat my cleaning. Sadly, I don't have an ultrasonic bath. How can I get the dust away which sticks on the PCB and the components?
I found the first "alive" signs. When I connected the power supply, I noticed that the led of the magsafe connector glowed very very dim.
I think that normally the connector should fade green and glow more brighter.
Macbooks are one of the easiest to find schematics on (next to Dells) because of their popularity... I don't know what exact model you have but e.g. try Googling "K36 MLB" which appears to be the '07 model. It's figuring out which parts are which on the non-silkscreened () PCB that is the main issue.
If you don't already have familiarity with PC architecture and its troubleshooting (because Macs are PCs now ) then this might be a good time to start learning... either way, give it a good clean first.
After you get it cleaned, then start checking the power rails first. Laptops have around a dozen but just start at the main ones (B+, V+ -- battery/DCIN) and work your way down to the standby rails, then the runs.
I forgot to mention that the lamp on the charger doens't light up when you plug it on the macbook.
That is controlled by the EC,which should be powered by one of the standby rails. You'll need to do more exploration from there, but the preliminary steps here are to make sure the standby subsystem (EC, charger, standby regulators) is all OK first.
That makes sense! I will try to start checking the powerrails. One problem I have is that I create very fast shorts with my multimeter probes. They are just too chunky. I switched to my scope which has smaller probe tips. The first thing I measured was the output of the power supply when its connected. The voltage drops down around every second/half a second (forgot my time/div setting).
Thank you for the links, I will try to get the green light glow bright first.