Tait TB7100, Service Manual

Page: 260 / 370

262 Transmitter Fault Finding (25W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 26 —
Output of Buffer in
Exciter Circuit
If the synthesizer output is correct, check the output at C313 of the buffer
amplifier in the exciter circuit.
1. If not already done, remove the
PAD TOP
can.
2. Enter the CCTM command
326 x
, where
x
defines the power level
selected in Task 25 .
3. Enter the CCTM command
101 x x 0
, where
x
is the frequency
selected in Task 25 .
4. Enter the CCTM command
33
to place the radio in transmit mode.
5. Measure the RF voltage after C313 (see Figure 13.15 ). (Use an
RFP5401A RF probe or the equivalent.) The required voltage
should be as given in
Table 13.8 (B1 band) or Table 13.9 (H5, H6).
6. Enter the CCTM command
32
to place the radio in receive mode.
7. If the voltage measured above is correct, go to Task 27 . If it is not, go
to Step 8 .
8. Check the components around Q300 (see Figure 13.15 ).
9. Repair any fault revealed by the above checks. Replace Q300
(see
Figure 13.15 ) if none of the other components is faulty.
10. Confirm the removal of the fault and go to “Final Tasks” on
page 123 . If the repair failed, replace the main-board assembly and go
to “Final Tasks” on page 123 .
Task 27 —
Output of Exciter
If the output of the buffer amplifier is correct, check that of the exciter at
C301.
1. With the radio still in transmit mode, measure the RF voltage after
C301
(see Figure 13.15 ). (Use an RFP5401A RF probe or the
equivalent.) The required voltage should be as given in Table 13.8
(B1 band) or Table 13.9 (H5, H6).
2. If the voltage is correct, go to Task 28 . If it is not, go to Step 3 .
3. Enter the CCTM command
32
to place the radio in receive mode.
4. Check the components between C313 and Q303, and between
Q303 and R308 (see
Figure 13.15 ).
5. Repair any fault revealed by the above checks. Replace Q303
(see
Figure 13.15 ) if none of the other components is faulty.
6. Confirm the removal of the fault and go to “Final Tasks” on
page 123 . If the repair failed, replace the main-board assembly and go
to “Final Tasks” on page 123 .