Tait TM8235, Руководство по обслуживанию

Страница: 278 / 578

278 Transmitter Fault Finding (40W/50W) TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
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 11.6 ). 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. The required values for the different frequency bands are
given in
Table 11.2 .
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 11.6 ).
12. If the power and current are now correct at all three frequencies, the
fault has been rectified; go to
“Final Tasks” on page 157 . If they are
not, go to Task 26 in “RF Signal Path” on page 303 .
RF output power: > 70W (VHF), > 60W (UHF)
current: < 15A (VHF), < 12A (UHF)