Tait TM8235, Руководство по обслуживанию

Страница: 357 / 578

TM8100/TM8200 Service Manual Transmitter Fault Finding (25W) 357
© Tait Electronics Limited June 2006
Task 22 —
Directional Coupler
and Buffer
Amplifier
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 buffer amplifier will be located.
1. Cycle the power.
2. Enter the CCTM command 326 5 to set the transmitter to maximum
power.
3. Enter the CCTM command 33 to place the radio in transmit mode.
4. Measure the voltage at pin 9 of IC303 in the power-control circuit
(see Figure 12.8 ).
5. The above voltage should be as given in Table 12.7 . If it is, go to
Task 24 . If it is not, go to Step 6 .
6. Check the voltage at pin 5 of IC303 (or use the
FWD PWR
test point )
(see Figure 12.8 ). Note that the probe impedance might affect the
measurement.
7. Enter the CCTM command 32 to place the radio in receive mode.
8. The voltage measured in Step 6 should be as given in Table 12.7 .
If it is not, go to Step 9 . If it is, go to Step 11 .
Table 12.7 Voltages at IC303 at maximum power (40 W)
Frequency band Frequency (MHz)
Voltage (V)
Pin 9 Pin 5 (
FWD PWR
)
A4 66
77
88 1.3 ± 0.5
1.5 ± 0.5
1.7 ± 0.5 1.1 ± 0.5
1.3 ± 0.5
1.4 ± 0.5
B1 136
155
174 2.2 ± 0.5
2.3 ± 0.5
2.5 ± 0.5 1.9 ± 0.5
2.1 ± 0.5
2.3 ± 0.5
C0 174
199.5
225 1.6 ± 0.5
1.8 ± 0.5
1.9 ± 0.5 3.0 ± 0.5
3.4 ± 0.5
3.7 ± 0.5
D1 216
241
266 2.2 ± 0.5
2.2 ± 0.5
2.3 ± 0.5 4.3 ± 0.5
4.3 ± 0.5
4.7 ± 0.5
H5 400
435
470 3.4 ± 0.5
3.8 ± 0.5
4.0 ± 0.5 3.3 ± 0.5
3.7 ± 0.5
3.9 ± 0.5
H6 450
490
530 3.9 ± 0.5
4.2 ± 0.5
4.7 ± 0.5 3.8 ± 0.5
4.1 ± 0.5
4.6 ± 0.5