IBM 3279 2A Maintenance Information page 14

1.2.3.1 Video Control Stritch
This switch has three positions:
1. Central position: The monitor receives the same
balance of color signals as the 3279 CRT.
2. ENHANCE position: The blue color of the
monitor
is
brightened by the addition of a
fifty-percent-green signal.
3. TEST position: The color signals to the monitor
are internally connected to the 3279 CRT, thus
allowing direct comparison of the two displays
(except for the separator line and Operator
Information Area).
1.2.3.2 Sync Polarity Stritcb
This switch
is
used to select either positive or
negative sync pulses at the sync output socket. All
devices attached at the same time will receive the
same polarity.
1.2.3.3 SIgDaI Test Indicator
This indicator lights when either
• The synchronizing signal
is
faulty,
or
• The Video Control Switch
is
set to TEST.
3279MfM
Chapter 1.
General
De8o;riptil>n and Location