September 5, 2008
6881076C25-E
4-52
Troubleshooting Procedures
: Power Amplifier Procedures
Methods of analyzing individual stages of the power amplifiers are detailed below. Most of the stages
are Class-C and must be analyzed under relatively high RF power levels. The following information
should help in isolation and repair of the majority of transmitter failures.
Testing Low-Level Amplifier (LLA) Circuitry
Proper operation of the LLA can be checked by monitoring the voltage across resistor R5805. The
voltage should measure in the range of 0.4 to 1.2 V, depending on the value of control voltage. A
0.4-V reading corresponds to a low control voltage (4 to 5 V) and a 1.2-V reading corresponds to a
high control voltage (up to control voltage limit).
Measure LLA voltages according to
Table 4-18
. If the DC bias conditions are correct, check to see if
the LLA is providing drive power to Q5803
.
Do so by checking Q5803 collector current under normal
drive conditions, as follows:
• Remove
R5810
and
L5806
(Be
sure to reinstall after testing).
• Solder wires to the remaining pads.
• Place an ammeter in series with Q5803 collector.
• Check for 0.2 to 0.5 A. (depending on control voltage).
NOTE:
With no RF drive to the input of the PA, Q5803 collector current should be zero.
NOTE:
The LLA voltages change with different control voltages. An example of LLA voltages with
control voltage equal to 10.0 V and 6 V is shown.
If Q5803 draws no current under normal conditions, then check for short or open input cable, or for
defective parts in the transmit injection filter or matching circuitry between Q5801 and Q5803.
Testing Second Stage Circuitry Q5803
The second stage is a typical class-C stage, except the base is biased with resistors R5809 and
R5806. The necessary conditions for proper operation of this stage are input drive power, and bias
conditions as shown in
Table 4-18
.
Table 4-18. LLA and 2nd Stage Typical Voltages
CONTROL
VOLTAGE
RF DRIVE OFF
RF DRIVE ON
10.0 V
6.0 V
10.0 V
6.0 V
Q5801
Base
Collector
–
0.7
8.1
–
0.7
9.1
–
0.7
8.0
–
0.3
8.8
Q5800
Base
Collector
Emitter
–
7.6
2.3
8.1
–
8.5
1.4
9.1
–
7.4
2.8
8.0
–
8.3
1.1
8.8
Q5806
Base
Collector
Emitter
–
6.4
7.6
5.7
–
3.8
8.5
3.2
–
6.4
7.4
5.7
–
3.9
8.3
3.2
Q5803
Base
Collector
–
0.6
9.6
–
0.6
9.6
–
0.0
9.5
–
0.3
9.5
Содержание ASTRO Digital Spectra
Страница 1: ...ASTRO Digital Spectra and Digital Spectra Plus UHF VHF 800 MHz Mobile Radios Detailed Service Manual ...
Страница 2: ......
Страница 6: ...September 5 2008 6881076C25 E iv Document History Notes ...
Страница 20: ...xviii List of Tables September 5 2008 6881076C25 E Notes ...
Страница 24: ...September 5 2008 6881076C25 E xxii CommercialWarranty Notes ...
Страница 48: ...September 5 2008 6881076C25 E xlvi Model Numbering Charts and Specifications Notes ...
Страница 142: ...September 5 2008 6881076C25 E 3 82 Theory of Operation Power Amplifiers Notes ...
Страница 218: ...September 5 2008 6881076C25 E 4 76 Troubleshooting Procedures Power Amplifier Procedures Notes ...
Страница 258: ...September 5 2008 6881076C25 E 6 14 Troubleshooting Waveforms ASTRO Digital Spectra Plus VOCON Board Waveforms Notes ...
Страница 434: ...September 5 2008 6881076C25 E Glossary 10 Notes ...
Страница 440: ...Index 6 September 5 2008 6881076C25 E Notes ...
Страница 441: ......