Tait TB7100, Service Manual

Page: 267 / 370

TB7100 Service Manual Transmitter Fault Finding (25W) 269
© Tait Electronics Limited October 2005
Task 32 —
Repair PIN switch
If the RF power at the PIN switch is low, the switch is not drawing the
expected current or the diode is faulty. Check the circuit as follows:
1. Perform a diode check of D307 (see Figure 13.17 ). If it is not faulty,
go to Step 2 . If it is, replace D307 and go to Step 3 .
2. Check the +9
V
0_
TX
supply to the PIN switch via the following
resistors on the bottom-side of the PCB (see Figure 13.18 ):
■
B1 band: R3080, R389 and R390
■
H5, H6 bands: R3000 and R389
If any resistor is faulty, replace the resistor as well as D307. (A faulty
resistor is likely to have resulted in damage to D307.)
3. With the test lead still connected to the test set, enter the CCTM
command
326 5
to set the transmitter power level to the maximum.
4. Enter the CCTM command 101 x x 0 , where x is the lowest
frequency (in hertz) for maximum power, as given in Table 13.8
(B1 band) or Table 13.9 (H5, H6).
5. Enter the CCTM command
33
to place the radio in transmit mode.
6. Again measure the RF output power. This should exceed 35 W.
7. Enter the CCTM command 32 to place the radio in receive mode.
8. Enter the CCTM command
101 x x 0
, where
x
is the highest
frequency (in hertz) for maximum power, as given in Table 13.8
(B1 band) or Table 13.9 (H5, H6).
9. Repeat Step 5 to Step 7 .
10. Remove the test lead and test capacitor, and resolder the blocking
capacitors C361, C362 and C363 (see
Figure 13.17 ) in position.
11. If the power in both the above cases is now correct, the fault has been
rectified; go to
“Final Tasks” on page 123 . If it is not, the repair
failed: replace the main-board assembly and go to “Final Tasks” on
page 123 .
RF output power: more than 35W