Tait TB7100, Service Manual

Page: 311 / 370

TB7100 Service Manual Transmitter Fault Finding (50W/40W) 313
© Tait Electronics Limited October 2005
Task 21 —
Check Power
Control
Check the power-control circuitry if the clamp current for the PA driver is
correct or if the voltage at the
SET PWR
test point is incorrect.
Important
Ensure that the current limit on the DC supply is 3 A.
And, when entering the CCTM command
304 z
, do not
specify a value z higher than that recorded in Task 12 . Fail-
ure to do so might result in the destruction of the PA driver.
1. Enter the CCTM command 304 z (where z was recorded in Task 12 ).
2. Note the current reading on the DC power supply.
3. Enter the CCTM command 114 0 to switch off the power.
4. Note the current reading on the DC power supply.
5. Compare the above current readings. The current should decrease by
an amount approximately equal to the offset given in
Table 14.6 .
If it does, go to Task 26 in “RF Signal Path” on page 321 . If it does
not, go to Step 6 .
6. Check that the voltage from the DAC is changing. Measure the
voltage at the
PWR
test point (
CDC TX PWR CTL
) (see Figure 14.11 and
Figure 14.12 ).
7. Enter the CCTM command
114 1023
. The voltage should increase
to:
8. Enter the CCTM command 32 to place the radio in receive mode.
9. If the voltage at the
PWR
test point increases as required, go to
Task 22 . If it does not, go to “CODEC and Audio Fault Finding” on
page 343 .
PWR test point: 2.4
±
0.1V