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Triggering Problems; Counter Frequencies; Trigger Mux Truth Table - HP 8560A Service Manual

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Triggering Problems

See function block H of A3 Interface Assembly Schematic Diagram (sheet 3 of 6).
The 1 MHz ADC clock provides synchronization in FREE RUN and SINGLE triggering.
LINE triggering synchronization originates on the A6 Power Supply. Trigger MUX A3U613A
selects between FREE RUN, VIDEO, LINE, and EXTERNAL trigger sources. The trigger
signal sets the output of the HSCAN latch high. HBADC-CLKO 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.
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 7-6 below.
2. If a trigger mode does not work, check that a trigger signal is present at the appropriate
MUX input, as indicated in Table 7-6.
Trigger Mode
FREE RUN
VIDEO
LINE
EXTERNAL
3. Check that the appropriate MUX input signal is present at the MUX output (A3U613
pin 7).
4. To check the video trigger level DAC, connect a DVM's positive lead to A3J400 pin 1 and
the negative DVM lead to A3TP4.
5. Press ITRIG) and VIDEO.
6. Press the STEP @ key several times while noting the DVM reading and position of the
video trigger level on the screen.
7. Check that the voltage displayed on the DVM increases by 1 V for each step of the VIDEO
TRIG LEVEL.
Table 7-5. Counter Frequencies
Table 7-6. Trigger MUX Truth Table
TRIG-SOURCE0
TRIG-SOURCE1
U613 pin 14
L
H
H
L
Nominal Frequency (Hz)
3900
1950
975
488
244
122
MUX Input
U613 pin 2
Pin Number U613
L
L
H
H
6
5
3
4

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