System Blue connector S1 3-4 ?

[elythomaslumber]

This is how I understand it too. Definitely do not jumper both 1-2 and 3-4, or you'll short the 5v input to the VDD output of IC501 and possibly damage ICs connected to VDD. I'm just guessing, but 5v is probably used on the E-field to counter voltage drop across the coax.

Thanks a lot! If it really can destroy the IC´s there should be some warning information added to the manual.