Many thanks Jochen,
I do not know why the latest questions I posted appear even earlier in the forum.
A solenoid is connected to a pair of screw terminals. Even the backplane is not powered by either DAQ device (in my case, motion controller) or external power supply, the solenoid is ALWAYS on. However, 2 mega-ohms can be detected from the screw terminal pair without solenoid connected.
Can it be off and how? If this is a problem of the backplane, what would possibly be the reasons?
If the LEDs can be turn on and off without any external power supply except the 7334 controller, does it mean the backplane can be powered by the controller?
I checked the Max. logic supply current for 70-ODC5 SSR modules is 14 mA in the Grayhill manufacture data sheet. And, are the LEDs needed to be considered as accessories as well? I cannot find how much power they consume from the original Grayhill documentation. What would be the current it requires?