Tait TM8100 mobiles Service Manual page 367

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 2A.
And, when entering the CCTM command 332 y, do not
specify a value y higher than that recorded in
Failure to do so might result in the destruction of the PAs.
1. Use the multimeter to measure the voltage at pin 8 of IC301
(see Figure 12.8). The voltage should be:
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.
Table 12.6.
Step 7. If the voltage
Task 17. If neither the current
Task 18.
Transmitter Fault Finding (25W)
Task 12.
Task 12).
367