318 Transmitter Fault Finding (40W/50W) TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
Task 3 4 —
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. Remove the
PIN TOP can.
2. Perform a diode check of D307 (VHF) or D3507 (UHF)
(see Figure 11.21). If it is not faulty, go to Step 3. If it is, replace
D307 or D3507, and go to Step 4.
3. Check the +9
V0_TX supply to the PIN switch via the following
resistors on the bottom-side of the PCB (see Figure 11.22 and
Figure 11.23):
■ VHF: R389 and R390
■ UHF: R3000, R389 and R390
If any resistor is faulty, replace the resistor as well as D307 (VHF) or
D3507 (UHF). (A faulty resistor is likely to have resulted in damage
to D307 or D3507.)
4. 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.
5. Enter the CCTM command 101 x x 0, where x is the lowest
frequency (in hertz) for maximum power, as given in Table 11.8
(B1), Table 11.9 (H5) or Table 11.10 (H7).
6. Enter the CCTM command 33 to place the radio in transmit mode.
Again measure the RF output power. This should be:
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 11.8
(B1), Table 11.9 (H5) or Table 11.10 (H7).
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 11.21) 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 157. If it is not, the repair
failed; replace the board and go to “Final Tasks” on page 157.
RF output power: more than 70W VHF)
more than 60W (UHF)
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