382 CODEC and Audio Fault Finding TM8100/TM8200 Service Manual
© Tait Electronics Limited June 2006
13.1 Power Supplies
Introduction First check that a power supply is not the cause of the fault. Of these
supplies, the 3.3V DC supply (+3
V3) will already have been checked in
“Power Supply Fault Finding” on page 163. The remaining supplies that
need to be checked are:
■ Task 1: 9V DC supply from 9V regulator (+9V0)
■ Task 2: 3V DC supply from 3V regulator (+3V0 AN)
■ Task 3: 2.5V DC supply from 2.5V regulator (+2V5 CDC)
Two other supplies used in the CODEC and audio circuitry are a 1.8V DC
supply (+1
V8) from the digital board and the 13.8V DC supply (+13V8 BATT)
from the power connector. Faults in these supplies are dealt with elsewhere.
Task 1 —
9V Power Supply
First check the 9V DC supply (+9V0), which is required by IC201.
1. Remove the board from the chassis.
2. Remove the
CDC BOT can.
3. Measure the voltage +9
V0 at pin 4 of IC201 (see Figure 13.1).
4. If the voltage is correct, go to Ta s k 2
. If it is not, go to Step 5.
5. The fault will be at IC201 (see Figure 13.1), since any fault with the
9V regulator in the PSU module will already have been rectified.
Therefore, check the soldering of IC201. Repair any fault.
6. Confirm the removal of the fault and go to “Final Tasks” on
page 157. If the repair failed or the fault could not be found, replace
the board and go to “Final Tasks” on page 157.
Task 2 —
3V Power Supply
If the 9V supply is correct, check the 3V DC supply (+3V0 AN) next.
1. Measure the voltage +3
V0 AN at the TP601 test point
(see Figure 13.1).
2. If the voltage is correct, go to Ta s k 3
. If it is not, go to Step 3.
3. The 3V regulator IC603 is suspect (see Figure 13.1). Check the
regulator as described in Ta sk 3
of “Power Supply Fault Finding” on
page 168.
pin 4 of IC201: 9.0 ± 0.3V DC
TP601 test point: 2.9 ± 0.3V DC
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