Trigon Dialog Owner's Manual page 12

The microprocessor checks which modules are available. There must always be at
least one input module and one output module present to ensure useful
configuration, otherwise you may get one of the following error messages:
A - No input module detected (above)
or
B - No otput module detected (below)
In either case please shut down and disconnect the preamplifier from AC mains and
verify that the respective modules are present and properly installed, or insert the
necessary module(s).
Make sure that at least one input module and one output module are installed!
With at least the minimum number of modules installed, the display will read as
shown in the following picture: