Explanation of the System Lock LEDs on the surface and iDR-16, iDR-32 and iDR-48 MixRacks.
Looking at a simple iDR-48 hooked up via ACE to an iLive-T112 with no external digital clocks:
MixRack System Lock LED ON indicates that the DSP audio is locked to the internal fixed clock.
MixRack System Lock LED OFF indicates that the DSP audio is not locked.
This could be due to the clock source being sourced externally via Port B, (user error - stored in scenes so potentially a scene recall could drop the internal sync) if there is no valid clock being sent to Port B you will not get system lock.
Scenes need to be checked to see that clock source is as required.
System Lock LED ON indicates that the surface audio is locked to the MixRack audio clock.
It is possible to have the rack LED OFF and the surface LED ON if the rack is assigned to external clock, but the external clock is not connected.
In this case, the rack LED is OFF because the rack cannot sync to the external clock but the surface LED is ON because it can sync to the rack internal clock.
System Lock LED OFF means that there is no valid audio link between the MixRack and the surface (e.g. connecting just via network not ACE).
This could be caused by cable error or maybe there is a hardware problem.
It gets more complex with the introduction of other clock sources but the principle is the same.
If the Lock LED is off there is a problem and you need to check the clock source setup.
NOTE: The surface Lock LED will not light if there is no ACE connection to the rack.
If there is only a network connection - there won't be any audio sync.