Tait TB7100, Service Manual

Page: 235 / 370

TB7100 Service Manual Transmitter Fault Finding (25W) 237
© Tait Electronics Limited October 2005
Task 10 —
Repair Output
Matching Circuitry
If the checks in Task 9 show that the power and current are still skewed,
there is a fault in the output matching circuitry.
1. If not already done, remove the
PAF TOP
can.
2. Check for faulty, shorted or misplaced components in the circuit
between the test capacitor and the common drain of Q309 and Q310
(see
Figure 13.6 to Figure 13.7 ). Repair any fault.
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.
4. Enter the CCTM command
33
to place the radio in transmit mode.
5. Note the RF output power measured by the test set, and note the
current reading on the DC power supply.
6. Enter the CCTM command 32 to place the radio in receive mode.
7. Program the radio with the centre frequency in the band: Enter the
CCTM command
101 x x 0 , where x is the frequency in hertz.
8. Repeat Step 4 to Step 6 .
9. Program the radio with the lowest frequency in the band: Enter the
CCTM command
101 x x 0
, where
x
is the frequency in hertz.
10. Repeat Step 4 to Step 6 .
11. Remove the test lead and test capacitor, and resolder the coupling
capacitors C348, C349 and C350 in position (see
Figure 13.6 to
Figure 13.7 ).
12. If the power and current are now correct at all three frequencies, the
fault has been rectified; go to
“Final Tasks” on page 123 . If they are
not, go to Task 25 in “RF Signal Path” on page 259 .
RF output power: > 35W
current: < 8A (VHF), < 9A (UHF)