Your issue is pretty simple. The default for the 1769-OF4 is -10 to 10VDC outputs. When you change it to 4-20 mA and leave it's raw proportional scaling (-32767-32767) the default for the out put data tag stays 0, or half scale, 12 mA. You need to change this under controller tags to -32767 on all 4 outputs. When you download all 4 outputs will be at 4mA. Then you can write code and modulate the output as you choose between 4-20mA.