Tait TM8100 mobiles Service Manual page 223

TM8100/TM8200 Service Manual
© Tait Electronics Limited November 2007
6. If the voltages are correct, go to
transmit buffer circuitry based on IC506 (see
repairs the fault, conclude with
7. Remove the
VCO BOT
8. Check the VCO buffer amplifier in receive mode. Enter the CCTM
command 335 1 to set the transmit-receive switch off.
9. Measure the voltage at the base of Q510 (see
base of Q510: 0V DC (receive mode)
10. Check the VCO buffer amplifier in transmit mode. Enter the CCTM
command 335 1 to set the transmit-receive switch on.
11. Measure the voltage at the base of Q510.
base of Q510: 0.7 ± 0.1V DC (transmit mode)
12. If the voltages are correct, the transmit VCO is suspect. Go to
Step 13. If they are not, check the VCO buffer circuitry based on
Q510 (see Figure
Step 14.
13. Check the transmit VCO circuitry based on Q509
(see Figure 9.11). Conclude with
14. 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
Step 7. If they are not, check the
Step 14.
can.
9.12). If this repairs the fault, conclude with
Step
"Final Tasks" on page
163.
Frequency Synthesizer Fault Finding
Figure 9.11). If this
Figure 9.12).
14.
163. If they are
"Final
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