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7. If the peak detector appears latched up, check LPOS-RST (U422 pin 4) for a negative
TTL level reset pulses. The reset pulses should occur every 130 ps and should be
approximately 250 ns wide.
8. If the reset pulses are absent, troubleshoot the Peak Detector Reset circuitry.
9. If the reset pulses are present, check the gate of Q207. 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 Q208 or CR203 or CR204.
Peak
Detector
Reset
Refer to function block R of A3 Interface Assembly Schematic Diagram in the
HP 8560 E-Series Spectrum Analyzer Component Level Information.
1. Press
(“1
on the spectrum analyzer and set the controls as follows:
Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..300MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
s
Detector mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . POS PEAK
2. Check that HHOLD (A3U526 pin 11) h
as 18 ps wide pulses every 128
pus.
3. Check that HODD (U408 pin 5) is a square wave with a period of 16.7 ms
(2 x sweep
time/600).
4. Check LPOS-RST (U422 pin 4) for 200 ns low-going pulses every 128
ps.
5. Check LNEG-RST (A3U422 pin 12) for 200 ns low-going pulses every 128 ps.
6. Set the detector mode to NORMAL and check that LNEG-RST (A3U422 pin 12) has two
pulses spaced 40 ps apart and then a single pulse approximately 88
/.LS
from the second
pulse.
7. Check HMUX-SELO (A3U408 pin 3)
and
HMUX-SELl
(A3U408 pin 9) according to
Table 8-8.
Table 8-8. HMUX-SELO/l versus Detector Mode
Detector Mode
HMUX-SELO
(U408
pin 3)
HMUX-SELl
(U408
pin 9)
NORMAL
15
ps
pulse every 128
ps
40
ps
pulse every 128 ps
SAMPLE
H
H
POS PEAK
H
L
NEG PEAK
L
H
8-20
ADC/lnterface
Section