Then it seems i have a handicapped version, i just looked at the PCB.
The - pin and + of RC of CN1 connector are both going to the optocoupler ... which is not present, on the top side of PCB there is silkscreen icon for it but the part is not there. Also the - pin of RC is not even getting there because there is a resistor on its way, there are pads for it but no part as well.
From what i see, later the signal should go to a jumper which is not present as well then to a switching transistor with a resistor and condensator on its way. All parts not present, while pads, silkscreen are present.