HP 8560E Service Manual page 365

ADC/Interface Section
Triggering or Video Gating Problems
5. Press and
TRIG VIDEO
6. Press the STEP
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 (IA0).
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 ,
PRESET
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
Center frequency ................................................ 300 MHz
Span ............................................................................ 0 Hz
Sweep time ............................................................. 150 ms
b. Press ,
TRIG EXTERNAL
until ON is underlined.
OFF
c. Press
GATE DLY [ ]
30 milliseconds.
LEN [ ]
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 HP
8560E/EC rear panel EXT/GATE TRIG INPUT and also (using a
BNC tee) to the channel 4 input of the oscilloscope (HP 54501A).
364
.
key several times while noting the DVM reading
, and
SWEEP DLY SWP ON OFF
30 milliseconds.
DLY SWP [ ]
and set the HP 8560E/EC as follows:
, then
SWEEP
10 milliseconds, then press
until ON is
and
GATE ON
GATE
Chapter 7