Tait TB7100, Service Manual

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TB7100 Service Manual Transmitter Fault Finding (50W/40W) 315
© Tait Electronics Limited October 2005
Task 22 —
Directional Coupler
and Buffer
Amplifiers
Following the checks in Task 19 to Task 21 , locate the fault and repair the
circuitry as described in the remaining tasks of the section. In this task any
faults in the directional coupler or the buffer amplifiers will be located.
1. Cycle the power.
2. Enter the CCTM command 326 5 to set the transmitter to maximum
power. Enter the CCTM command
33
to place the radio in transmit
mode.
3. Measure the voltage at pin 9 of IC303 in the power-control circuit
(see
Figure 14.11 and Figure 14.12 ).
4. The above voltage should be as given in Table 14.7 . If it is, go to
Task 24 . If it is not, go to Step 5 .
5. Check the voltage at the
FWD PWR
test point (pin 5 of IC303) and at
the
REV PWR
test point (pin 3 of IC303) (see Figure 14.11 and
Figure 14.12 ). Note that the probe impedance might affect these
measurements.
6. Enter the CCTM command
32
to place the radio in receive mode.
7. The voltages measured in Step 5 should be as given in Table 14.7 .
If they are, go to Step 10 . If the
FWD PWR
voltage is incorrect, go to
Step 8 . If the
REV PWR
voltage is incorrect, go to Step 9 .
8. Remove the
DIRC TOP
can. Check the components of the directional
coupler (see Figure 14.17 ) and go to Step 11 .
9. Remove the
DIRC TOP
can. Check D305 and R3035 (B1) or R383
(H5, H7) (see Figure 14.17 ). If there is no fault, the PIN switch or
LPF or both are suspect; go to Task 33 . If there is a fault, go to
Step 11 .
10. In the buffer amplifiers, check R340 and R341 (see Figure 14.11 ,
Figure 14.18 and Figure 14.19 ).
Table 14.7 Voltages at IC303 at maximum power (70 W for B1 band, and 60W for H5 and H7)
Frequency band Frequency (MHz)
Voltage (V)
Pin 9 Pin 3 (
REV PWR
) Pin 5 (
FWD PWR
)
B1
136
155
174
2.6 ± 0.5
2.9 ± 0.5
3.2 ± 0.5
0.4 ± 0.3
0.4 ± 0.3
0.5 ± 0.3
3.1 ± 0.5
3.4 ± 0.5
3.9 ± 0.5
H5
400
435
470
2.8 ± 0.5
3.0 ± 0.5
3.3 ± 0.5
0.6 ± 0.4
0.6 ± 0.4
0.5 ± 0.4
3.3 ± 0.5
3.7 ± 0.5
3.9 ± 0.5
H7
450
485
520
3.9 ± 0.5
4.1 ± 0.5
4.4 ± 0.5
0.6 ± 0.4
0.8 ± 0.4
0.8 ± 0.4
4.4 ± 0.5
4.6 ± 0.5
5.0 ± 0.5