344
Transmitter Fault Finding (25W)
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
Task 13 —
Check Biasing
of First PA
Check the biasing of the first PA (Q310).
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
Failure to do so might result in the destruction of the PAs.
1.
Use a multimeter to measure the voltage at pin 14 of
IC301
(see
). The voltage should be:
2.
Note the current reading on the DC power supply. As mentioned in
, this will be less than 500mA.
3.
Enter the CCTM command
331
x
(where
x
was recorded in
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
6.
If the voltage and current are both correct, go to
. If the voltage
is correct but not the current, go to
. If neither the current
nor the voltage is correct, go to
7.
Enter the CCTM command
331 1
to switch off final bias 1, and go to
.
pin 14 of IC301: < 100mV (initially)
pin 14 of IC301: 2 to 5V (after entry of CCTM 331
x
)
Table 12.6
Gate biases for the PAs and PA driver at high power
Frequency band
Offset currents in mA
First PA
Second PA
PA driver
A4
750
750
300
B1
750
750
300
C0
750
750
300
D1
800
800
300
H5
1000
1000
450
H6
1000
1000
450
Содержание TM8235
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