Tait TB7100, Service Manual

Page: 332 / 370

334 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 32 —
Repair Circuitry
If the RF output power measured in Task 31 is low, there is a fault in the
circuit between the common drain of the PAs and the test capacitor.
1. If not already done, remove the
PAF TOP
can.
2. Check for faulty, shorted or misplaced components in the circuit
between the test capacitor and the common drain of Q309 and Q310
(see
Figure 14.8 and Figure 14.9 ).
3. Repair any fault revealed by the above checks and go to Step 5 . If no
fault could be found, go to Step 4 .
4. Remove the test lead and test capacitor, resolder the coupling
capacitors C348, C349 and C350 in position (see
Figure 14.25 ),
and go to Task 26 .
5. With the test lead still connected to the test set, enter the CCTM
command
326 5 to set the transmitter power level to the maximum.
6. Enter the CCTM command
101 x x 0
, where
x
is the lowest
frequency (in hertz) for maximum power, as given in Table 14.8
(B1 band), Table 14.9 (H5) or Table 14.10 (H7).
7. Enter the CCTM command 33 to place the radio in transmit mode.
8. Measure the RF output power. This should be:
9. Enter the CCTM command 32 to place the radio in receive mode.
10. Enter the CCTM command
101 x x 0
, where
x
is the highest
frequency (in hertz) for maximum power, as given in Table 14.8
(B1 band), Table 14.9 (H5) or Table 14.10 (H7).
11. Repeat Step 7 to Step 9 .
12. Remove the test lead and test capacitor, and resolder the coupling
capacitors C348, C349 and C350 in position (see
Figure 14.25 ).
13. If the power in both the above cases is now correct, the fault has been
rectified; go to
“Final Tasks” on page 123 . If it is not, the repair
failed; replace the main-board assembly and go to “Final Tasks” on
page 123 .
RF output power: more than 70W (B1 band)
more than 60W (H5, H7 bands)