HP 8562E, Service Manual

Page: 284 / 482

3. Check that the appropriate trigger MUX input signal is present at the trigger MUX
output pin 7).
4. To check the video trigger level DAC, connect the positive lead of a DVM to pin 1
and the negative DVM lead to
5. Press (TRIG) and .
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 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 pin 4).
b. While using the front-panel knob to adjust the video trigger level, check for the
presence of pulses on pin 15 (LDAC2).
c. While using the front-panel knob to adjust the video trigger level, check for the
presence of pulses on pin 16 (LWRCLK).
d. Check that pulses are present on 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 pin but the
instrument does not appear to be sweeping, proceed as follows:
a. Press and SWP OH OFF
DLY 30 milliseconds.
until ON is underlined, then
b. Using an oscilloscope, check for activity at pins 1 and 3 of
c. If there is activity at pin 1 but not at pin 3 of suspect or
d. If there is activity at pin 1 and pin 3 of suspect (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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Span
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150ms
b. Press , then and until ON is underlined.
Press GATE
DLY
10 milliseconds, then press LEN 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 and a
frequency of 10 Hz.
8-10 Section