HP 8560A, Руководство по обслуживанию

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8. If the reset pulses are absent, troubleshoot the Peak Detector Reset circuitry.
9. If the reset pulses are present, check the gate of The pulses should be positive-going
from -12.7 V to -1.35 V.
10. The peak detector can be made into a unity gain amplifier by shorting the cathode of
CR203 to the anode of CR204. If the peak detector functions normally as a unity gain
amplifier, suspect or CR203 or CR204.
Peak Detector Reset
See function block R of A3 Interface Assembly Schematic Diagram (sheet 4 of 6).
1. Press on the HP 8560A and set the controls as follows:
C E N T E R F R E Q . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SPAN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Hz
SWEEP TIME . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5s
DETECTOR MODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POS PEAK
2. Check that HHOLD pin 11) has 18 wide pulses every 128
3. Check that HODD pin 5) is a square wave with a period of 16.7 ms
(2 x sweep
4. Check (U422 pin 4) for 200 ns low-going pulses every 128
5. Check LNEG_RST pin 12) for 200 ns low-going pulses every 128
6. Set the detector mode to NORMAL and check that LNEG_RST pin 12) has two
pulses spaced 40 apart and then a single pulse approximately 88 from the second
pulse.
7. Check pin 3) and pin 9) according to
Table 7-8.
Table 7-8. Versus Detector Mode
Detector Mode
NORMAL
40
pulse every 128
SAMPLE H
POS PEAK H
NEG PEAK L
40
pulse every 128
H
L
H
Rosenfell Detector
See function block S of A3 Interface Assembly Schematic Diagram (sheet 4 of 6).
If both and are high during the same bucket,
HROSENFELL will also be set high. This indicates that the video signal probably consists of
noise, since it rose and fell during the same period. The HROSENFELL signal is valid only
when the NORMAL ( rosenfell) detector mode is selected.
7-18 Section