Merlin 3070 Service And Maintenance Manual page 177

PHYSICAL FEATURES
The Diagnostics Module, color-coded orange, occupies slot 4 in the
control unit. (When the Diagnostics Module is not used, a plastic
cover protects slot 4.)
EIA RS-232c jack: Permits connection
of a data terminal.
4-character alphanumeric display:
Provides diagnostic messages during
testing.
Normal/Test switch: Permits normal
call processing when set to Normal;
permits diagnostic testing when set to
Test.
Next pushbutton: Pressed to resume
testing when diagnostics are
interrupted to indicate a fault.
Detail pushbutton: Pressed to request
further information when "*" appears
in the alphanumeric display, signaling
detection of a problem.
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