Tait TM8100 mobiles, Руководство по обслуживанию

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388 Transmitter Fault Finding (25W) TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
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 12.16 ).
3. Solder one terminal of a test capacitor to the PCB at the point shown
in
Figure 12.16 . Mount the capacitor vertically. Use a test capacitor
of the type GRM111, DLI C17, Murata 1210, or the equivalent.
The value of the capacitor depends on the frequency band of
the radio:
■
A4 — 100pF
■
B1, C0, D1 — 680pF
■
H5, H6 — 82pF.
4. Solder a 50
Ω
test lead to the PCB. Solder the outer sheath in the
position shown in Figure 12.16 , 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 12.8
(A4), Table 12.9 (B1), Table 12.10 (C0), Table 12.11 (D1) or
Table 12.12 (H5, H6).
8. Enter the CCTM command
33
to place the radio in transmit mode.
9. Measure the RF output power. This should exceed 35W.
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 12.8
(A4), Table 12.9 (B1), Table 12.10 (C0), Table 12.11 (D1) or
Table 12.12 (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