Tait TM8000 Series Service Manual page 229

Task 11 —
Check Power at
Directional Coupler
TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
9. Measure the RF voltage at the gates of the PAs Q309 [at 3F3/3E5]
and Q310 [at 3F2/3D5] (see
RF voltage is present, go to Task 11. If there is no RF voltage,
check the components of the interstage matching circuitry
between the PA driver Q306 and the gates of the PAs (see
Figure 9.25 and
the removal of the fault, and return to
failed or the fault could not be found, return to
and replace the complete main-board assembly.
If, as determined in Task 10, there is no fault in the initial RF signal path,
investigate the remainder of the circuitry: the directional coupler, PIN
switch, and LPF. Check the directional coupler as follows:
1. Remove the
DIRC TOP
2. Remove the coupling capacitors C348, C349, C350 [at 3K3/3E9]
(see Figure 9.27
3. Solder one terminal of an 82 pF (B1 band) or 680 pF (D1, H5,
H6) test capacitor to the PCB at the point shown in
and Figure 9.28. Mount the capacitor vertically. Use a test
capacitor of the type GRM111, DLI C17, Murata 1210, or the
equivalent.
Solder a 50 Ω test lead to the PCB. Solder the outer sheath to the
4.
test pad shown in
central wire to the other terminal of the test capacitor.
5. Connect the test lead to the test set and measure the RF output
power. This should exceed 35 W. If it does, remove the test lead
and test capacitor, resolder the coupling capacitors in position, and
go to Task 12. If it does not, go to Step 7.
6. Check for an open circuit between the test capacitor and the
common drain of Q309 [at 3F3/3E5] and Q310 [at 3F2/3D5] (see
Figure 9.18 and
Figure 9.28). Also check for faulty, shorted or misplaced
components in this part of the circuit. Repair any fault.
7. Again measure the RF output power. If it is correct, the fault has
been rectified; if it is not, the repair failed. Remove the test lead
and test capacitor, resolder the coupling capacitors in position, and
return to Subsection
complete main-board assembly.
Figure 9.18
Figure 9.26). If a fault is found, repair it, confirm
Subsection
can.
and Figure 9.28).
Figure 9.27 and Figure
Figure 9.19 as well as
8.1. If the repair had failed, replace the
Diagnosis of Faults on Main Board
and Figure 9.19). If an
8.1. If the repair
Subsection 8.1
Figure 9.27
9.28, and solder the
Figure 9.27 and
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