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374 CODEC and Audio Fault Finding TM9100 Service Manual

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 13.1).

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 13.1). Check the

regulator as described in Task 3

of “Power Supply Fault Finding” on

page 158.

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

Tait TM9100 Service Manual

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