Tait TM8100 mobiles, Руководство по обслуживанию

Страница: 255 / 620

TM8100/TM8200 Service Manual Receiver Fault Finding 255
© Tait Electronics Limited November 2007
10.3 Moderate or Slight Loss of Sensitivity
Introduction
This section covers the case where the receiver has suffered a moderate or
slight loss of sensitivity. As measured in Task 1, the receiver gain will be less
than 500 000, but not as low as 1500. With a gain less than 40 000, the loss
of sensitivity will be moderate — about 15dBm too low; otherwise it will
be slight — just a few decibels too low. There are three tasks:
■
Task 7 : front-end calibration and tuning voltages (all bands except K5)
■
Task 8 : moderately low receiver sensitivity
■
Task 9 : slightly low receiver sensitivity
The fault-diagnosis procedures of Task 8 and Task 9 are similar; although
the differences are minor they are important.
Task 7 —
Front-end
Calibration
and Tuning Voltages
(all bands except
K5)
If the loss of sensitivity is moderate or slight, the fault is probably in the
front-end tuning circuitry. This task is for all bands except K5. For the K5
band, go to
Task 8 on page 256 .
1. Using the calibration application, check the calibration of the front-
end tuning circuitry: Open the
“Raw Data”
page and click the
“Receiver”
tab.
2. Record the values listed in the
“Rx FE Tune BPF Settings”
field — these
are the DAC values of the FE (front-end) tuning voltages for the five
frequencies
FE TUNE0
to
FE TUNE4
.
(
FE TUNE0
is the lowest frequency and
FE TUNE4
the highest fre-
quency in the radio’s frequency band; the values are given in
Table 10.2 .)
3. For each of the frequencies FE TUNE0 to FE TUNE4 in turn, carry out
the following procedure: Enter the CCTM command
101 a a 0
,
where
a
is the frequency in hertz.
Enter the CCTM command
376
and record the value returned — this
is the in millivolts.
4. Compare the values measured in Step 2 and Step 3 with the nominal
DAC and voltage values listed in Table 10.2 .
5. If the DAC and voltage values are correct, go to Step 8 . If they are
not, go to Step 6 .
6. Recalibrate the receiver using the calibration application, and check
the DAC and voltage values again.
7. If the DAC and voltage values are now correct, the fault has been
rectified; go to
“Final Tasks” on page 163 . If they are not, go to
Step 8 .
8. Go to Task 8 if the receiver output level x measured in Task 1 was less
than 40 000; otherwise go to Task 9 .