346 CODEC and Audio Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 3 —
2.5V Power Supply
If the 9V and 3V supplies are correct, the remaining power supply to check
is the 2.5V DC supply (+2
V5 CDC).
1. Measure the voltage +2
V5 CDC at pin 5 of IC604 (see Figure 15.1).
2. If the voltage is correct, go to Step 4. If it is not, go to Step 3.
3. The 2.5V regulator IC604 is suspect (see Figure 15.1). Check the
regulator as described in Task 3
of “Power Supply Fault Finding” on
page 132.
4. Proceed to the section relevant to the fault exhibited:
■ “Faulty Speaker Audio” (distorted or no speaker audio)
■ “No Speaker Audio at Auxiliary Connector” (no speaker audio at
auxiliary connector)
■ “Faulty Receiver” (receiver does not operate)
■ “Faulty Modulation” (distorted or no transmit modulation)
■ “Faulty Modulation Using Auxiliary Connector” (modulation at
auxiliary connector only)
Further details are given in the introduction to the section.
pin 5 of IC604: 2.5 ± 0.3V DC
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