Just a note on battery damage and how it can affect the physical properties of PCB's and solder. Firstly it can penetrate underneath the solder mask (the green protective layer) and eat away at the copper, it then spreads as far and wide as it can, through traces and vias (the holes that travel between PCB layers, front to back) When acid comes into contact with solder (on component legs or in vias) it seems to eat away the lead and just leave a crumbly crud which doesn't conduct electricity anymore. So it is really important to replace this crumbly crud with fresh solder, but - as it isn't proper solder anymore it can be super difficult to remove, it takes a lot of time and patience.
Coloured in purple are the affected areas that will need work
You can see the acid has traveled all the way up to the chip legs, this means the traces and vias will be extremely weak and I will need to be extremely careful when removing the chip for cleaning the area
Acid had travelled down to the ram expansion bus, so this will also require removing extremely carefully and cleaning
As mentioned before, the solder on these resistor legs are crud and so they need lifting and the vias need cleaning. I also scraped away the corrosion on the copper layer underneath the old battery and put a layer of solder over it. Normally I'd use clear over-coat but I don't have any at the moment! The diodes and resistor in the audio section also needed patching together since the trace was gone.
Expansion header removed, ready for cleaning
Chip removed, ready for cleaning
A nice bath in the ultrasonic for the expansion pins and chip
Chip socketed, as at this point I can't be 100% sure the chip works and therefore installing a socket is important
As you can see, there is light shining through these vias now, where as before they were full of grey crud
All the broken traces are now patched up!
All working, yay!