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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
DLY
SWP
[
1
30 milliseconds.
until ON is
underlined, then
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.
8-10
ADC/lnterface
Section