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.
3. Check that the appropriate MUX input signal is present at the MUX output (A3U613
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
Table 7-5. Counter Frequencies
Table 7-6. Trigger MUX Truth Table
U613 pin 14
Nominal Frequency (Hz)
U613 pin 2
Pin Number U613