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
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