Tait TM8100 mobiles Service Manual page 222

Task 27 —
Check Transmit
Buffer Amplifier
222 Frequency Synthesizer Fault Finding
If no transmit frequency is detected but the switching network is not faulty,
check the transmit buffer amplifier. If the amplifier is not faulty, there might
be a fault in the transmit VCO that was not detected earlier.
For all bands except K5:
1. Remove the
VCO BOT
2. Check the transmit buffer amplifier in receive mode: Enter the
CCTM command 335 0 to set the transmit-receive switch off.
3. Measure the voltage at pin 6 of Q5001 (see
pin 6 of Q5001: 0V DC (receive mode)
4. Check the transmit buffer amplifier in transmit mode: Enter the
CCTM command 335 1 to set the transmit-receive switch on.
5. Measure the voltage at pin 6 of Q5001.
pin 6 of Q5001: 0.7 ± 0.1V DC (transmit mode)
6. If the voltages are correct, the transmit VCO is suspect; go to
If they are not, the transmit buffer amplifier is suspect; go to
7. Remove the
VCO TOP
8. Check the transmit VCO circuitry based on Q510
(see Figure 9.11). Conclude with
9. Check the buffer circuitry based on Q5001 (see
10. If a fault is found, repair the circuit, and confirm that the voltages are
now correct. If they are, go to
not, or if no fault could be found, replace the board and go to
Tasks" on page
For the K5 band:
1. Remove the
SYN TOP
2. Check the transmit buffer amplifier in receive mode: Enter the
CCTM command 335 0 to set the transmit-receive switch off.
3. Measure the voltage at pin 4 of IC506 (see
pin 6 of IC506: 0V DC (receive mode)
4. Check the transmit buffer amplifier in transmit mode: Enter the
CCTM command 335 1 to set the transmit-receive switch on.
5. Measure the voltage at pin 4 of IC506.
pin 4 of IC506: 5 ± 0.1 V DC (transmit mode)
can.
can.
Step
"Final Tasks" on page
163.
can.
© Tait Electronics Limited November 2007
Figure 9.12).
Step
Step
10.
Figure 9.12).
163. If they are
"Final
Figure 9.11).
TM8100/TM8200 Service Manual
7.
9.