Chapter 8 385
ADC/Interface Section
Triggering or Video Gating Problems
Triggering or Video Gating Problems
Refer to function block H of A3 Interface Assembly Schematic Diagram
(sheet 3 of 6) in the 8560 E-Series Spectrum Analyzer Component Level
Information.
The 1 MHz ADC clock provides synchronization in FREE RUN and
SINGLE triggering. LINE triggering synchronization originates on the
A6 power supply. Trigger MUX A3U613 selects between FREE RUN,
VIDEO, LINE, and EXTERNAL trigger sources. The trigger signal sets
the output of the HSCAN latch high. HBADC_CLK0 provides the
trigger signal for FREE RUN. The VIDEO TRIG signal must be at least
25 mV (0.25 divisions) peak-to-peak to trigger in video trigger mode.
The 3 MHz video bandwidth is not available when using video gating.
The trigger for Gated Video has two modes of operation, level mode and
edge mode. In the edge mode, positive-edge or negative-edge triggering
can be selected. Output 0 from pin 10 of A3U617 generates the gate
delay and output 1 from pin 13 of A3U617 generates the gate length.
The duration of these two time intervals is set using front-panel
softkeys under the
SWEEP key. The trigger input for Gated Video is the
rear panel EXT/GATE TRIG INPUT (TTL > 10 kΩ).
1. Check that the trigger MUX is receiving the proper trigger source
information by selecting each of the following trigger modes and
checking the TRIG_SOURCE0 and TRIG_SOURCE1 lines as
indicated in Table 8-5 below.
2. If a trigger mode does not work, check that a trigger signal is present
at the appropriate trigger MUX input, as indicated in Table 8-5.
3. Check that the appropriate trigger MUX input signal is present at
the trigger MUX output (A3U613 pin 7).
4. To check the video trigger level DAC, connect the positive lead of a
DVM to A3J400 pin 1 and the negative DVM lead to A3TP4.
5. Press
TRIG and VIDEO.
6. Press the STEP
▼ key several times while noting the DVM reading
and position of the video trigger level on the screen.
Table 8-5 Trigger MUX Truth Table
Trigger Mode TRIG_SOURCE0
U613 pin 14
TRIG_SOURCE1
U613 pin 2
MUX Input Pin
Number U613
FREE RUN L L 6
VIDEO H L 5
LINE H H 3
EXTERNAL L H 4
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