Disconnected wire unit between the Signal Backplane and the LPS module (reference 4, LPS side and reference 5 Signal backplane side image "Mains and CTRL connection LPS").

Reconnect the wire unit between the Signal Backplane and the LPS module.

Disconnected wire unit between the “CTLB IN” and “CTLB OUT” sockets of the LPS units (reference 3 image "Mains and CTRL connection LPS").

Reconnect the wire unit between the “CTLB IN” and “CTLB OUT” sockets of the LPS units.

Malfunction of one of the LPS units. The orange LED (Heartbeat) of the malfunction LPS is not blinking.

Replace the whole LPS module. See "Removing the LPS module".

Defect Signal Backplane.

Replace the Signal Backplane. See "Replacement of the signal back plane".