352
Transmitter Fault Finding (25W)
TM8100/TM8200 Service Manual
© Tait Electronics Limited
June 2006
Task 19 —
Biasing of
PA Driver—
DRV
test point
If there is no fault in the biasing of the PAs, investigate the biasing of the PA
driver (Q306). First check the
DRV
test point.
Important
Ensure that the current limit on the DC supply is 2A.
And, when entering the CCTM command
304
z
, do not
specify a value
z
higher than that recorded in
Failure to do so might result in the destruction of the PA
driver.
1.
Note the current reading on the DC power supply. As mentioned in
, the current will be less than 500mA.
2.
Enter the CCTM command
304
z
(where
z
was recorded in
)
to switch on the clamp current.
3.
Note the current reading on the DC power supply.
4.
Compare the above current readings. The current should increase by
an amount approximately equal to the offset given in
If it does, go to
. If it does not, go to
.
5.
Check as follows that the voltage from the DAC is changing:
First enter the CCTM command
304 1
to switch off the bias.
6.
Measure the voltage at the
DRV
test point
(
CDC
TX
DRV
BIAS
)
(see
). The voltage should be:
7.
Enter the CCTM command
304
z
(where
z
was recorded in
)
to change the DAC value of the clamp current.
8.
The voltage should increase to:
9.
If the voltage does change, go to
. If it does not, go to
10.
Enter the CCTM command
32
to place the radio in receive mode,
and go to
“CODEC and Audio Fault Finding” on page 381
.
DRV test point: < 0.1V (after entry of CCTM 304 1)
DRV test point: 0.8 to 2.5V (after entry of CCTM 304
z
)
Содержание TM8235
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