Tait TM9100 Service Manual

350 Transmitter Fault Finding (25W Radios) TM9100 Service Manual
© Tait Electronics Limited August 2005
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 12.9).
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 12.9). 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.
9. Remove the
DIRC TOP can.
10. Check the components of the directional coupler (see Figure 12.12)
and go to Step 12.
11. Check R340 between pins 6 and 7 of IC303 in the buffer amplifier
(see Figure 12.13), and then go to Step 12.
12. Repair any fault revealed by the above checks. Replace IC303 if none
of the other components is faulty (see Figure 12.9).
Table 12.7 Voltages at IC303 at maximum power (40 W)
Frequency band Frequency (MHz)
Voltage (V)
Pin 9 Pin 5 (
FWD PWR)
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
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

Tait TM9100 Specifications

General

Brand	Tait
Model	TM9100
Category	Radio
Language	English