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premodulator operation and switched filter operation controlling that band as shown
in Table 6D-1. If the problem is not frequency dependent and if the level is accurate
above +7 dBm but inaccurate below +7 dBm, the Attenuator/ RPP Assembly is likely
at fault.
If the level problem is not in a particular frequency band, it is advisable to troubleshoot
at a low frequency where an oscilloscope is useful. Put the instrument in a known state
by selecting SPCL01, set the frequency to 88 MHz, and set the amplitude to +13 dBm.
The voltage at TP8 on the modulation control PCA should be +1.3 ± .5V DC. If this
voltage is correct, the problem is localized to the Output PCA following the detector
diode CR20 or the Attenuator/RPP assembly. The appropriate signal levels following
this point are:
R121
Q7 base
Q7 collector
CR23 cathode
Q9 base
Q9 collector
Q16 collector
These voltages are approximate and are as measured with a 10 megohms, 8 pF,
oscilloscope probe using a ground connection made at the probe tip with less than 1
inch of lead.
Table 6D-1. Band, Filter, and Frequency Programming Data
FREQUENCY (MHz)
.01-
14.999999
15-
21.999999
22-
31.999999
32-
46.999999
47-
63.999999
64-
127.999999
128- 179.999999
180- 255.999999
256- 349.999999
350- 511.999999
512- 624.999999
625- 729.999999
730-1056.000000
0.9V p-p
0.4V p-p
0.85V p-p
0.82V p-p
At 88 MHz.
0.6V p-p
1.5V p-p
3.0V p-p
F
F
F
F
G
G
1
2
3
4
T
T
5
2
2
7
6
1
2
3
4
6
4
8
2
2
7
4
0
0
0
0
0
1
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
1
0
0
0
0
0
1
1
0
0
0
0
1
1
0
0
0
0
1
1
0
0
0
0
1
1
0
0
0
0
1
1
0
0
0
0
1
1
TROUBLESHOOTING AND REPAIR
G
G
1
2
3
4
T
T
H
H
H
H
2
6
A
A
A
A
5
2
F
F
F
F
6
5
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
1
0
0
0
0
1
0
0
0
0
0
1
0
0
0
0
1
0
0
0
0
1
0
0
0
0
0
1
0
0
0
1
0
1
0
0
0
1
0
1
0
0
0
1
0
1
0
0
0
1
1
1
0
0
0
1
1
1
0
0
0
RF LEVEL/AM
M
H
H
I
A
E
D
O
T
C
T
1
0
1
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
0
0
1
1
0
1
0
0
0
0
0
0
0
0
0
1
0
6D-7
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