Theory of Operation—2246 1Y and 2246 Mod A Service
hysteresis is increased so that a larger signal
change is required to produce a state change at the
output of the comparators. Trigger Coupling control
logic is shown in Table 3-6.
Another signal source selectable in the Trigger
Coupling Selectors is the output of the TV Trigger
Detector (TV LINE or TV FIELD). An applied com
posite video signal is separated so that the hori
zontal line or vertical field sync pulse can be used to
trigger the oscilloscope for Television signal display
(see TV Trigger Detector description). Selection
between LINE or FIELD for the A Trigger source is
done by multiplexer U1104A with its output being
applied to pin 18 of U421B. Pin 18 of U431B in the B
Trigger system has an input of either the TV Line
sync signal, for TV triggering of the B Sweep, or the
output of the Measurement Signal Low-Pass Filter,
when the DC measurement mode is active.
Table 3-6
Trigger Selection Logic
Front Panel
Latched Bit Values
Description
Coupling
Selection
SLOPE
TS2
TS1
TSO
A Sweep Mode (U421) AUTO LEVEL, AUTO, NORM, or SGL SEQ
DC
0
0
1
0
DC Coupled
NOISE REJ
1
0
1
0
DC Coupled, Noise Reject
HF REJ
0
1
0
1
HF Reject
LF REJ
0
0
1
1
LF Reject
AC
0
1
0
0
AC Coupled
A Sweep Mode (U421) TV LINE or TV FIELD
DC
1
0
0
0
TV Input, Noise Reject
NOISE REJ
1
0
0
0
TV Input, Noise Reject
HF REJ
1
0
0
0
TV Input, Noise Reject
LF REJ
1
0
0
0
TV Input, Noise Reject
AC
1
0
0
0
TV Input, Noise Reject
B Sweep Mode (U431) AUTO LEVEL, RUNS AFTER or NORM
DC
0
0
1
0
DC Coupled
NOISE REJ
1
0
1
0
DC Coupled, Noise Reject
HF REJ
0
1
0
1
HF Reject
LF REJ
0
0
1
1
LF Reject
AC
0
1
0
0
AC Coupled
B Sweep Mode (U432) TV LINE
DC
1
0
0
0
TV Input, Noise Reject
NOISE REJ
1
0
0
0
TV Input, Noise Reject
HF REJ
1
0
0
0
TV Input, Noise Reject
LF REJ
1
0
0
0
TV Input, Noise Reject
AC
1
0
0
0
TV Input, Noise Reject
3-13
Summary of Contents for 2246 1Y
Page 13: ...2246A Service 7062 01 X The 2246 1Y or 2246 Mod A Portable Oscilloscope ...
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