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1. Set the spectrum analyzer to the following settings:
Center frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..300MHz
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . OHz
Reference level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -10
dBm
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50s
DETECTORMODE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . SAMPLE
2. Refer to Table 8-9 and check for correct logic levels at A3U108 pins 1, 15, and 16. Check
for proper output signals at TP6. If the select lines are not changing, suspect the ADC
ASM or the VGA/ADC MUX Control. If the select lines are changing, but the proper
video inputs are not being switched to the output, replace
U108.
In SAMPLE mode, the
input is MOD-VIDEO (pin 7); in POS PEAK mode, the input is
POS-PEAK
(pin 5);
and in NEG PEAK mode, the input is
NEG-PEAK
(pin 6).
3. Check for the presence of the YTO ERR signal at A3J2 pin 42 with an oscilloscope probe.
4. If ERR 300 YTO UNLK or 301 YTO UNLK occurs and the voltage is near zero during a
sweep and positive during retrace (YTO is being locked), the fault is on the A3 assembly.
If a constant dc voltage is present, refer to the synthesizer troubleshooting procedure in
Chapter 11, “Synthesizer Section.”
Table 8-9. Logic Levels at
A3U108
Detector Mode
U108
pin 1
U108
pin 15
U108
pin 16
SAMPLE
H
L
H
POS PEAK
H
L L
NEG PEAK
L
L
H
5. Set the spectrum analyzer to the following settings:
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...5 MHz
Sweep time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50ms
6. Check for the presence of the SCAN RAMP signal by connecting an oscilloscope probe to
A3J2 pin 45 (component side of
A3J2).
C
onnect
the negative-probe lead to
A3TP4.
7. A 0 to 10 V ramp should be present in both LINE and FREE RUN trigger modes. If the
waveform is present only in LINE trigger, ADC control signal HBADC-CLKO may be
faulty. Refer to “ADC Control Signals” in this chapter.
8. If the scan ramp is present, but is not being switched to the output of U108, replace
U108.
If the scan ramp is absent in either mode, do the following:
a. Connect the oscilloscope probe to A3J400 pin 15 (HSCAN).
b. A TTL signal (high during 50 ms sweep time and low during retrace) should be
present, indicating A3 is working properly. Refer to the synthesizer troubleshooting
procedure in Chapter 11, “Synthesizer Section.”
A faulty TTL signal indicates a bad
A3 Interface assembly.
9. Set the spectrum analyzer to the following settings:
Sweeptime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
100ms
Span . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
..lOOMHz
8-22
ADC/lnterface
Section