Tait TB7100, Service Manual

Page: 241 / 370

TB7100 Service Manual Transmitter Fault Finding (25W) 243
© Tait Electronics Limited October 2005
Task 14 —
Shaper and
Level Shifter
If the voltage measured in Task 13 is correct but not the current, either the
first PA or the shaper and level shifter for the PA is suspect.
Important
Ensure that the current limit on the DC supply is 2 A.
And, when entering the CCTM command
331 x
, do not
specify a value x 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
331 x
(where
x
was recorded in Task 12 ).
6. Check that the voltage at the gate of Q310 is (see Figure 13.10 ):
7. Enter the CCTM command 32 to place the radio in receive mode.
8. If the voltage measured above is correct, Q310 is faulty; replace the
main-board assembly and go to
“Final Tasks” on page 123 . If it is not
correct, go to Step 9 .
9. Check the circuitry between pin 14 of IC301 and the gate of Q310
(see
Figure 13.10 ). 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 Q310 itself is faulty, replace the main-board assembly and go to
“Final Tasks” on page 123 .
gate of Q310: 2 to 5V