Refer to your schematic of Post#3, the 1uF capacitor between Pin-2 and GND of MAX232 is my concern. According to MAX232 data sheets the negative terminal of the capacitor could be terminated either to GND or Vcc (5V).
The internal 5V/+/-10V converter of MAX232 develops about +8 to +10V) at Pin-2. I have chosen in my design (MPU/MCU Trainers) to terminate the -ve side of the capacitors at Vcc (5V) while the ratings of all the 1uF filter capacitors are 16V.