Tait TM8100 mobiles, Service Manual

Page: 256 / 620

256 Receiver Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
Task 8 —
Moderately Low
Sensitivity
For all bands except K5, following the initial investigation in Task 7 , check
the circuitry as follows when the sensitivity loss is moderate. For the K5
band, these steps start
on page 257 .
All bands except K5:
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 3V supply voltage at L404 ; use the measurement point
shown in Figure 10.3 .
4. Also check the LNA bias conditions. First measure V
c
between the
collector of Q401 and ground (see Figure 10.3 ).
5. Secondly, check I
c
. To do so, unsolder and raise one terminal of L404
(tombstone position) (see Figure 10.3 ), connect a multimeter
between this terminal and the pad for the terminal, and measure the
current.
6. If the checks in Step 2 to Step 5 reveal no fault, go to Step 7 . If there
is a fault, repair it and go to Step 8 .
7. Check the signal level at the output of LO1 and continue the fault
diagnosis as in
“Power Supply for FCL” on page 234 .
8. Recalibrate the receiver using the calibration application.
9. Confirm the removal of the fault and go to “Final Tasks” on
page 163 . If the repair failed, go to Task 9 .
V
c
: 2.7 ± 0.1V
I
c
: 10 ± 1mA