TB7100 Service Manual Frequency Synthesizer Fault Finding 151
© Tait Electronics Limited October 2005
Task 4 —
6V Power Supply
If the output of the SMPS is correct, check the 6V DC supply next.
1. Measure the supply +6
V0 at pin 4 of IC606 (see Figure 11.2).
2. If the voltage is correct, go to Task 5
. If it is not, measure the 9V
input at pin 5 of IC606 (see Figure 11.2).
3. If the voltage is correct, go to Step 4. If it is not, the 9V regulator
IC601 is suspect; go to Task 3
of “Power Supply Fault Finding” on
page 132.
4. If the input to the regulator IC606 is correct but not the output,
check IC606 (see Figure 11.2) and the associated circuitry; if
necessary, replace IC606.
Remove the
SYN TOP can and check the C-multipliers Q508 (pins 3,
4, 5) and Q512 for shorts (see Figure 11.2); replace any suspect
transistor.
5. If a fault is found, repair the circuit, confirm the removal of the fault,
and go to “Final Tasks” on page 123. If the repair failed or no fault
could be found, replace the main-board assembly and go to “Final
Tasks” on page 123.
pin 4 of IC606: 6.0 ± 0.3V DC
pin 5 of IC606: 9.0 ± 0.3V DC
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