Tait TB7100 - Page 292

294 Transmitter Fault Finding (50W/40W) TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 9 —
Power and Current
Are Skewed
If the RF output power and the supply current are skewed, the output
matching is suspect.
1. Remove the
DIRC TOP can.
2. Remove the coupling capacitors C348, C349 and C350 —
see Figure 14.8 (B1) and Figure 14.9 (H5, H7).
3. Solder one terminal of an 82 pF (H5, H7 bands) or 680 pF (B1) test
capacitor to the PCB at the point shown in Figure 14.8 and
Figure 14.9. Mount the capacitor vertically. Use a test capacitor of
the type GRM111, DLI C17, Murata 1210, or the equivalent.
4. Solder a 50 Ω test lead to the PCB. Solder the outer sheath to the test
pad shown in Figure 14.8 and Figure 14.9, and solder the central
wire to the other terminal of the test capacitor.
5. Connect the test lead to the test set.
6. 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.
7. Enter the CCTM command 33 to place the radio in transmit mode.
8. Note the RF output power measured by the test set, and note the
current reading on the DC power supply.
9. Enter the CCTM command 32 to place the radio in receive mode.
10. 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.
11. Repeat Step 7 to Step 9.
12. 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.
13. Repeat Step 7 to Step 9.
14. If the power and current are still skewed, go to Task 10
. If the power
and current are correct, remove the test lead and test capacitor,
resolder the coupling capacitors in position, and go to Task 33
— the
PIN switch and LPF require checking.
RF output power: > 70W (VHF), > 60W (UHF)
current: < 15A (VHF), < 12A (UHF)