Tait TP9100 - Page 232

232 Transmitter Fault Finding TP9100 Service Manual
© Tait Electronics Limited May 2005
Task 10 —
Check Biasing
of PA
Check the biasing of the PA (Q106).
Important Ensure that the current limit on the DC supply is 2A. And,
when entering the CCTM command 331 x, do not specify
a value x higher than that recorded in Task 9. Failure to do
so might result in the destruction of the PAs.
1. Use a multimeter to measure the voltage at pin 14 of IC101
(see Figure 10.7). The voltage should be:
2. Note the current reading on the DC power supply. As mentioned in
Step 5 of Task 9, this will be less than 550mA.
3. Enter the CCTM command 331 x (where x was recorded in Task 9).
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 10.5.
6. If the voltage and current are both correct, go to Step 7. If the voltage
is correct but not the current, go to Ta s k 1 1
. If neither the current
nor the voltage is correct, go to Tas k 12
.
7. Enter the CCTM command 331 1 to switch off final bias 1, and go to
Ta sk 1 4
.
pin 14 of IC301: < 100mV (initially)
pin 14 of IC301: 2 to 5V (after entry of CCTM 331 x)
Table 10.5 Gate biases for the PA at high power
Frequency band PA offset current in mA
B1 600
H5 800
H6 900