C (gcc), 132 128128 109
i;m;x;y;fi;m;f(char*s){x=*s-64-(*s>73);y=atoi(s+1);forfor(i=380;i--;putchar(m?m==20m^84-x&&i*s+(*s>73)|(i/20+1==y20+1)^atoi(s+1)?79:m%6==4&&im%6^4|i/20%6==320%6^3?46:42:4679:10))m=i%20;} A function that prints the board to STDOUT. Requires the letter coordinate to be capital. Printing in one loop seems to be slightly shorter than the previous nested loop approach.