Answer to "iPhone 5S Stuck in recovery mode : iTunes restore error 50"It is indeed a baseband issue. But baseband ic cannot be replaced.
Answer to "How to remove epoxy resin on mainbaord?"H2SO4 will be helpfull.
Answer to "Water damage, backlight not working!"First (when charging) the iphone is off, only the charging circuit and display are working. Important is that the battery is not connected at this stage, except for charging. Now, when the apple logo appears, the iphone is connected to and powered by the battery. The battery has a connection, which gives the battery temperature. It is possible that if this is faulty and the iphone thinks it is to hot (battery) and won't turn the backlight on (which would heat up the battery even more). So, in short, try a new battery..