Tait TB7100, Service Manual

Page: 305 / 370

TB7100 Service Manual Transmitter Fault Finding (50W/40W) 307
© Tait Electronics Limited October 2005
Task 17 —
Shaper and
Level Shifter
If the voltage measured in Task 16 is correct but not the current, either the
second PA or the shaper and level shifter for the PA is suspect.
Important
Ensure that the current limit on the DC supply is 3 A.
And, when entering the CCTM command
332 y
, do not
specify a value y higher than that recorded in Task 12 .
Failure to do so might result in the destruction of the PAs.
1. If the
PAF TOP
can has already been removed, go to Step 5 . If it has
not, go to Step 2 .
2. Enter the CCTM command 32 to place the radio in receive mode.
3. Remove the
PAF TOP
can.
4. Enter the CCTM command 33 to place the radio in transmit mode.
5. Enter the CCTM command
332 y
(where
y
was recorded in Task 12 ).
6. Check that the voltage at the gate of Q309 is (see Figure 14.13 and
Figure 14.14 ):
7. Enter the CCTM command
32
to place the radio in receive mode.
8. If the voltage is correct, Q309 is faulty; replace the main-board
assembly and go to
“Final Tasks” on page 123 . If it is not, go to
Step 9 .
9. Check the circuitry between pin 8 of IC301 and the gate of Q309
(see
Figure 14.13 and Figure 14.14 ). If a fault is found, repair it,
confirm the removal of the fault, and go to “Final Tasks” on
page 123 . If the repair failed or Q309 itself is faulty, replace the main-
board assembly and go to “Final Tasks” on page 123 .
gate of Q309: 2 to 5V