There is a small battery in the CDC four which supports the control parameters when mains power is removed, this battery needs replacing roughly every 12 months ( FAQ: How do I replace the back-up battery in a CDC four). When the battery is replaced it is necessary to “power cycle” the CDC four twice to re-establish a set of default parameters.
It has been noted that sometimes after doing this the CDC four will no longer communicate with a stage rack (this issue does not happen with the later CDC four:m version of the console). This communication issue is a result of the CDC four incorrectly resetting itself to use “Legacy MegaCOMMS mode” due to a memory corruption.
The quickest and easiest way to clear this problem is to do a firmware update, either via a Net Update or using a USB Memory Stick. This will clear the corruption of the Legacy parameter and restore communications to the stage rack.
If for any reason you do not want to do a firmware upgrade then another way to clear the problem would be:
You should now find that communications with the stage box will be restored.