Tait TB7100, Service Manual

Page: 234 / 370

236 Transmitter Fault Finding (25W) 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 13.6 (B1), and Figure 13.7 (H5, H6).
3. Solder one terminal of an 82 pF (H5, H6 bands) or 680 pF (B1) test
capacitor to the PCB at the point shown in
Figure 13.6 to
Figure 13.7 . 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 13.6 to Figure 13.7 , 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 31 — the
PIN switch and LPF require checking.
RF output power: > 35W
current: < 8A (VHF), < 9A (UHF)