Tait TM8100 mobiles - Page 367

TM8100/TM8200 Service Manual Transmitter Fault Finding (25W) 367
© Tait Electronics Limited November 2007
Task 16 —
Check Biasing
of Second PA
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 Task 12.
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:
2. Note the current reading on the DC power supply. As mentioned in
Step 7 of Tas k 1 2
, the current will be less than 500mA.
3. Enter the CCTM command 332 y (where y was recorded in Task 12
).
4. Check that the voltage changes to:
5. Also note the current reading. This should increase by an amount
approximately equal to the offset given in Table 12.6.
6. If the voltage and current are both correct, go to Step 7. If the voltage
is correct but not the current, go to Tas k 17
. If neither the current
nor the voltage is correct, go to Tas k 1 8
.
7. Enter the CCTM command 332 1 to switch off final bias 2, and go to
Task 19
.
pin 8 of IC301: < 100mV (initially)
pin 8 of IC301: 2 to 5V (after entry of CCTM 332 y)