Tait TB7100, Service Manual

Page: 221 / 370

TB7100 Service Manual Transmitter Fault Finding (25W) 223
© Tait Electronics Limited October 2005
Task 1 —
13.8V Power Supply
First check the power supply from the power connector.
1. Obtain a needle probe to use for measurements of the power supply
at the PA driver and PAs. If none is available, remove the
PAF TOP
and
PAD TOP
cans.
2. Set the DC power supply to 13.8 V, with a current limit of 9A.
3. Program the radio with the highest frequency in the radio’s frequency
band: Enter the CCTM command
101 x x 0 , where x is the frequency
in hertz. The required values for the different frequency bands are
given in
Table 13.2 .
4. Enter the CCTM command
326 5
to set the radio to maximum
power.
5. Attempt to place the radio in transmit mode. Enter the CCTM
command
33 .
6. If the radio enters the transmit mode, continue with Step 7 . If instead
a C03 error is displayed in response to the command 33 , go to Task 7
in “Transmitter RF Power” on page 232 .
7. Measure the voltage at the point on L310 shown in Figure 13.2 .
This is the supply at the common drain of Q309 and Q310, and
should be:
8. Also measure the voltage at the point on L306 shown in
Figure 13.3 . This is the supply at the drain of Q306, and should be:
9. Enter the CCTM command
32
to place the radio in receive mode.
10. If the power supply measured in Step 7 and Step 8 is not correct, go
to Task 2 . If it is, go to Task 3 .
common drain of Q309 and Q310: more than 13V DC
drain of Q306: more than 13V DC