Tait TB7100, Service Manual

Page: 306 / 370

308 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 18 —
Shaping Filter for
Power Control
If neither the voltage nor the current measured in Task 16 is correct, then
the shaping filter for the power-control circuitry or the CODEC and audio
circuitry is suspect.
Important
Ensure that the current limit on the DC supply is 3A.
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. Use the multimeter to measure the voltage at the
FIN
2
test point
(see Figure 14.11 and Figure 14.12 ). The voltage should be:
2. Enter the CCTM command 332 y (where y was recorded in Task 12 ).
3. Check that the voltage changes to:
4. Enter the CCTM command
32
to place the radio in receive mode.
5. If the voltage measured above is correct, go to Step 6 . If it is not, go
to “CODEC and Audio Fault Finding” on page 343 .
6. Check IC301 and the surrounding shaping-filter circuitry
(see
Figure 14.11 and Figure 14.12 ). 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, replace the main-board assembly and go
to “Final Tasks” on page 123 .
FIN2 test point: 18
±
2V (initially)
FIN2 test point: 1.1 to 2.7V (after entry of CCTM 332 y )