Tait TM8100 mobiles, Service Manual

Page: 386 / 620

386 Transmitter Fault Finding (25W) TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 28 —
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 (A4, B1, C0) or after C317 and C389 (D1, H5, H6)
(see Figure 12.14 ). (Use an RFP5401A RF probe or the equiva-
lent.) The required voltage should be 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).
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 C301 and Q306
(see Figure 12.14 ).
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 360 .
6. Repair the fault. Confirm the removal of the fault and go to “Final
Tasks” on page 163 . If the repair failed, replace the board and go to
“Final Tasks” on page 163 .
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 12.15 ).
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 29
. 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 12.15 ).
13. If a fault is found, repair it, confirm the removal of the fault, and go
to
“Final Tasks” on page 163 . If the repair failed or the fault could
not be found, replace the board and go to “Final Tasks” on page 163 .