Theory of Operation—2213 Service
CHANNEL 2 SOURCE. When S305 is set to CH 2, the
LO logic level present on S305 pin B is coupled to pin A
and applied to U305D pin 12 and to U305C pin 10. The
output of U305C at pin 8 is a LO which is applied to the
CH 2 Trig signal line by the wired-AND connection. When
the CH 2 Trig signal is LO, the Channel 1 Internal Trigger
Pickoff Amplifier is biased o ff to prevent the Channel 1
signal from reaching the Internal Trigger Amplifier.
The inputs to U305B, pins 4 and 5, are both pulled HI
through R305 and R304 respectively, and the HI output
from pin 6, applied to the wired-AND connection on the
CH 1 Trig signal line, allows U315C to control the CH 1
Trig signal logic level. As described in the preceding "Chan
nel 1 Source" discussion, the logic levels at U305D pins 12
and 13 control the output of U315B. The LO on U305D
pin 12 ensures a LO output at pin 11, which is applied to
U315C at pin 9. This LO ensures a HI output at U315C
pin 8, the CH 1 Trig signal line.
With the CH 1 Trig signal HI, Q273 in the Channel 2
Trigger Pickoff Amplifier is biased on and the Channel 2
signal is passed on to the Internal Trigger Amplifier.
VERT MODE SOURCE. Additional switch settings are
involved in determining the internal trigger signal selection
when VERT MODE Trigger Source is selected. Both the
CH 1-BOTH-CH 2 and the ADD-ALT-CHOP VERTICAL
MODE switches establish the vertical signal display and, as
3-11
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