Tait TM8000 Series, Руководство по обслуживанию

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TM8100 Mobile Radio Service Manual Diagnosis of Faults on Main Board 213
May 2004 © Tait Electronics Limited
Task 5 —
Prepare to Check
Biasing
If the transmitter is not being inhibited, check the biasing of the two PAs
and the PA driver. First make the following preparations:
1. Set the current limit on the DC power supply to 2 A.
2. Use the calibration application to determine the bias offset current
for the first PA: Open the
“Final Gate Bias 1” page, click the “Set”
button and, under the
“Target Current”
label, note the offset current
(in mA) in the “High Power” field.
3. Repeat Step 2 to find the offset current for the second PA on the
“Final Gate Bias 2” page.
4. Also find the offset current for the PA driver: Open the
“Tx Driver
Bias Limit” page, click the “Set” button, and note the offset current
(in mA) in the
“Target Current”
field.
5. Enter the CCTM command 331 to check the DAC value of final
bias 1 (
CDC TX FIN BIAS
1
) at maximum power. Record the value
a
returned.
6. Enter the CCTM command
332
to check the DAC value of final
bias 2 (
CDC TX FIN BIAS
2
) at maximum power. Record the value
b
returned.
7. Enter the CCTM command
304
to check the DAC value of the
clamp current at the driver gate. Record the value
c
returned.
8. Enter the CCTM command 33 to place the radio in transmit
mode.
9. Turn off all biases by entering the following CCTM commands in
sequence:
■
331 1
■
332 1
■
304 1
■
114 1023
■
334 0
■
335 0
10. Note the current reading on the DC power supply. This will be
about 300 mA.