Tait TM8000 Series Service Manual page 203

Task 4 —
Receiver Sensitivity Is
Few Decibels Too Low
Table 9.4 Nominal AGC data
Parameter
AGC voltage (mV)
B1 frequency band
D1 frequency band
H5 frequency band
H6 frequency band
Receiver input power (dBm)
Standard radio
Trigger-base radio
TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
If the receiver sensitivity is just a few decibels too low, the fault-diagnosis
procedure is similar to that of Task 3.
1. Using the calibration application, check the calibration of the
front-end tuning circuitry: Open the "Raw Data" page and click
the "Receiver" tab. Record the values listed in the "Rx FE Tune BPF
Settings" field — these are the DAC values of the FE tuning
voltages for the five frequencies FE TUNE0 to FE TUNE4.
(FE TUNE0 is the lowest frequency and FE TUNE4 the highest
frequency in the radio's frequency band.)
For each of the frequencies FE TUNE0 to FE TUNE4 in turn, carry
2.
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 front-
end tuning voltage in millivolts.
3. Compare the values measured in Steps 1 and 2 with the nominal
DAC and voltage values listed in
correct, go to Step 4. If they are not, recalibrate the receiver using
the calibration application, and check the DAC and voltage values
again. If the values are now correct, the fault has been rectified;
return to Subsection
4. Remove the
FE TOP
components of the front-end tuning circuitry from C400 [at
4B6/4G1] to T401 [at 4L6/4G10] (see
Figure 9.15). Also check the LNA and IF-amplifier bias
conditions as in Step 4 of Task 3 and Step 5 of Task 2 respectively.
If there is no fault, go to Step 5. If there is, repair the fault and go
to Step 6.
5. Check the PIN switch and LPF as in Task 9 and Task 10 of
Subsection 9.6
6. Recalibrate the receiver using the calibration application.
Confirm the removal of the fault and return to
the repair failed, return to
complete main-board assembly.
AGC voltages and receiver input powers
AGC0
2110 ± 50
2050 ± 50
2200 ± 50
2220 ± 50
–68
–62
Table
8.1. If they are not, go to Step 4.
and cans. Check the soldering of all the
IF TOP
on the transmitter.
Subsection 8.1
AGC1
1960 ± 40
1900 ± 40
2040 ± 40
2050 ± 40
–60
–54
Diagnosis of Faults on Main Board
9.3. If the values are
Figure 9.13 and
Subsection 8.1. If
and replace the
AGC2
1790 ± 40
1750 ± 40
1860 ± 40
1870 ± 40
–50
–44
203