The majority of balcony problems exist due to the entry of water at weak points in the construction, weakening the interior frame work. The balcony in turn begins to shift or bow when weight is applied, causing concrete to crack, eventually allowing more and more water to enter and begin the interior frame damaging phase.
Cracked concrete should be repaired immediately upon discovery to stop water penetration, making sure all flashing is sealed as well as any posts or bolts pentrating the concrete. All stairwells attached to the balcony should be self supported.
Demo damaged concrete to existing deck, inspect all deck for damage or weakness. Demo soffit below to inspect interior frame work. Repair all frame work and decking as needed to support new balcony construction. Install flashing at all required areas. Install a water tight membrane to existing deck, creating a "shower pan effect", prior to pouring new concrete. Install support post where necessary.