TB7100 Service Manual Transmitter Fault Finding (25W) 265
© Tait Electronics Limited October 2005
Task 29 —
Check Power at
Directional Coupler
If, as determined in Task 25 to Task 28, there is no fault in the initial RF
signal path, investigate the final signal path. This part of the circuitry may
also require investigation following certain checks in “Transmitter RF
Power”. Begin by checking the directional coupler as follows:
1. If not already done, remove the
DIRC TOP can.
2. Remove the coupling capacitors C348, C349, C350
(see Figure 13.24).
3. Solder one terminal of an 82pF (H5, H6 bands) or 680pF (B1) test
capacitor to the PCB at the point shown in Figure 13.24. Mount the
capacitor vertically. Use a test capacitor of the type GRM111, DLI
C17, Murata 1210, or the equivalent.
4. Solder a 50Ω test lead to the PCB: Solder the outer sheath to the test
pad shown in Figure 13.24, and solder the central wire to the other
terminal of the test capacitor.
5. Connect the test lead to the test set.
6. Enter the CCTM command 326 5 to set the transmitter power level
to the maximum.
7. Enter the CCTM command 101 x x 0, where x is the lowest
frequency (in hertz) for maximum power, as given in Table 13.8
(B1 band) or Table 13.9 (H5, H6).
8. Enter the CCTM command 33 to place the radio in transmit mode.
9. Measure the RF output power. This should exceed 35 W.
10. Enter the CCTM command 32 to place the radio in receive mode.
11. Enter the CCTM command 101 x x 0, where x is the highest
frequency (in hertz) for maximum power, as given in Table 13.8
(B1 band) or Table 13.9 (H5, H6).
12. Repeat Step 8 to Step 10.
13. If the power measured in both the above cases exceeds 35W, go to
Step 14. If it does not, go to Task 30
.
14. Remove the test lead and test capacitor, resolder the coupling
capacitors in position, and go to Task 31
.
RF output power: more than 35W
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