TB7100 Service Manual Transmitter Fault Finding (50W/40W) 329
© Tait Electronics Limited October 2005
Task 30 —
Output of PA Driver
If the exciter output is correct, check the output of the PA driver at the
drain of Q306. If necessary, also check the signal at the gates of the PAs
Q309 and Q310. This is the last point in the initial RF signal path.
1. With the radio still in transmit mode, measure the RF voltage at the
drain of Q306 (B1 — see Figure 14.21) or after C317 and C389
(H5, H7 — see Figure 14.22). (Use an RFP5401A RF probe or the
equivalent.) The required voltage should be as given in Table 14.8
(B1), Table 14.9 (H5) or Table 14.10 (H7).
2. Enter the CCTM command 32 to place the radio in receive mode.
3. If the voltage measured above is correct, go to Step 7. If it is not, go
to Step 4.
4. Check the components between C307 and Q306 (see Figure 14.21
and Figure 14.22).
5. If the above checks reveal a fault, go to Step 6. If they do not, go to
Task 12
in “Biasing of PA Driver and PAs” on page 297.
6. Repair the fault. 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.
7. If not already done, remove the
PAF TOP can.
8. Enter the CCTM command 326 5 to set the power level to the
maximum, and then the command 33 to place the radio in transmit
mode.
9. Measure the RF voltage at the gates of the PAs Q309 and Q310
(see Figure 14.23 and Figure 14.24).
10. Enter the CCTM command 32 to place the radio in receive mode.
11. If an RF voltage is present, there is no fault in the initial RF signal
path; go to Task 31
. If there is no RF voltage, go to Step 12.
12. Check the components of the interstage matching circuitry between
the PA driver Q306 and the gates of the PAs Q309 and Q310
(see Figure 14.23 and Figure 14.24).
13. If a fault is found, repair it, confirm the removal of the fault, and go
to “Final Tasks” on page 123. If the repair failed or the fault could
not be found, replace the main-board assembly and go to “Final
Tasks” on page 123.
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