Agilent Technologies 856290216 service manual 10 ADC/lnterface Section

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 BIDE0 .

6.Press the STEP II] 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 changes by 1 V for each step of the VIDEO TRIG LEVEL.

8.If the voltage changes incorrectly, proceed as follows:

a.Check the -10 Vdc reference (A3U409 pin 4).

b.While using the front-panel knob to adjust the video trigger level, check for the presence of pulses on A3U409 pin 15 (LDAC2).

c.While using the front-panel knob to adjust the video trigger level, check for the presence of pulses on A3U409 pin 16 (LWRCLK).

d.Check that pulses are present on U409 pin 6 (IAO).

9.If the LWRCLK and LDAC2 signals are not correct, refer to “Interface Strobe Select” in this chapter.

10.If correct trigger pulses are present at the trigger MUX output (A3U613 pin 7), but the instrument does not appear to be sweeping, proceed as follows:

a. Press (-1, (SWEEP), and DLY SWP OH OFF until ON is underlined, then

DLY SWP [ 1 30 milliseconds.

b. Using an oscilloscope, check for activity at pins 1 and 3 of A3U615A.

c. If there is activity at pin 1 but not at pin 3 of A3U615A, suspect A3U616 or A3U617.

d. If there is activity at pin 1 and pin 3 of A3U615A, suspect A3U615. (Check pin 5 for activity.)

11.If there is a problem with Video Gating, proceed as follows: a. Press (PRESET) and set the spectrum analyzer as follows:

Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..300MHz Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150ms

b. Press LTRIG), EJE’SERNAL , then (5) and GATE DN 0FF until ON is underlined.

c. Press GATE DLY E ] 10 milliseconds, then press GATE LEN I: 3 30 milliseconds.

d. Connect a pulse/function generator (such as an HP 8116A) to provide a 5 V peak-to-peak square wave (TTL level) to the spectrum analyzer rear-panel EXT/GATE TRIG INPUT and also (using a BNC tee) to the channel 4 input of the oscilloscope (HP 54501A).

e. Set the pulse/function generator to NORMAL mode with a duty cycle of 50%) and a frequency of 10 Hz.

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