Sony CA-590 - Manual (Page 13)

Internal Boards and Switch Settings
13
A S1 switch
Selects the signal to be output to the RETURN connector.
RET: Return video signal is output (factory-setting).
MONI: Monitor video signal is output.
VBS: Composite video signal is output.
B S2 switch
Selects the signal to be input/output from the PROMPTER
connector.
PROMPT: Prompter video signal is input and output
(factory-setting).
REF: Reference signal for the video camera is input.