Tait TM8100 mobiles Service Manual page 299

Task 16 —
Check Biasing
of Second PA
TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
If the biasing of the first PA is correct, check that of the second PA (Q309).
Important
Ensure that the current limit on the DC supply is 3A.
And, when entering the CCTM command 332 y, do not
specify a value y higher than that recorded in
Failure to do so may result in the destruction of the PAs.
1. Use the multimeter to measure the voltage at pin 8 of IC301
(see Figure 11.9
pin 8 of IC301: < 100mV (initially)
2. Note the current reading on the DC power supply. As mentioned in
Step 7 of Task 12, the current will be less than 500mA.
Enter the CCTM command 332 y (where y was recorded in
3.
4. Check that the voltage changes to:
pin 8 of IC301: 2 to 5V (after entry of CCTM 332 y)
5. Also note the current reading. This should increase by an amount
approximately equal to the offset given in
6. If the voltage and current are both correct, go to
is correct but not the current, go to
nor the voltage is correct, go to
Enter the CCTM command 332 1 to switch off final bias 2, and go to
7.
Task 19.
and Figure 11.10). The voltage should be:
Task
Task 18.
Transmitter Fault Finding (>25W)
Task 12.
Task
Table 11.6.
Step 7. If the voltage
17. If neither the current
12).
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