Tait TM8100 mobiles - Page 258

258 Receiver Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
6. Check the signal level at the output of LO1 and continue the fault
diagnosis as in “Power Supply for FCL” on page 234.
7. Confirm the removal of the fault and go to “Final Tasks” on page 163
on page 136. If the repair failed, go to Task 9
.
Task 9 —
Slightly Low
Sensitivity
Following the initial investigation in Task 7, check the circuitry as follows
when the sensitivity loss is slight.
1. Remove the
FE TOP can and, if not already done, the IF TOP can.
2. Check the soldering of all the components of the front-end tuning
circuitry from C400 to T401 (see Figure 10.1 and Figure 10.3).
3. Check the IF-amplifier bias conditions as in Step 4 and Step 5 of
Task 5
.
4. Check the LNA bias conditions as in Step 4 and Step 5 of Tas k 8
.
5. If the checks of Step 2 to Step 4 reveal no fault, go to Step 6. If there
is a fault, repair it and go to Step 7.
6. Check the PIN switch and LPF as in Task 31
to Task 33 of
“Transmitter Fault Finding (>25W)” on page 267 or “Transmitter
Fault Finding (25W)” on page 341.
7. Recalibrate the receiver using the calibration application.
8. 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.
Table 10.3 Front-end tuning voltages and corresponding DAC values (K5 band)
Frequency band
Tuning voltages at five different frequencies
FE TUNE0 FE TUNE1 FE TUNE2 FE TUNE3 FE TUNE4
K5 band
Frequency (MHz)
DAC value
Voltage (V)
761.9
0
0
776.1
0
0
849.9
255
3.0
860.1
255
3.0
870.1
255
3.0