Tait TB7100, Руководство по обслуживанию

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344 CODEC and Audio Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
15.1 Power Supplies
Introduction
First check that a power supply is not the cause of the fault. Of these
supplies, the 3.3 V DC supply (
+3
V
3
) will already have been checked in
“Power Supply Fault Finding” on page 127 . The remaining supplies that
need to be checked are:
■
Task 1 : 9 V DC supply from 9V regulator ( +9
V
0 )
■
Task 2 : 3 V DC supply from 3V regulator (
+3
V
0
AN
)
■
Task 3 : 2.5 V DC supply from 2.5V regulator ( +2
V
5
CDC
)
Two other supplies used in the CODEC and audio circuitry are a 1.8V DC
supply (
+1
V
8 ) from the digital board and the 13.8 V DC supply ( +13
V
8
BATT
)
from the power connector. Faults in these supplies are dealt with elsewhere.
Task 1 —
9V Power Supply
First check the 9V DC supply ( +9
V
0 ), which is required by IC201.
1. Remove the main-board assembly from the chassis.
2. Remove the
CDC BOT
can.
3. Measure the voltage +9
V
0 at pin 4 of IC201 (see Figure 15.1 ).
4. If the voltage is correct, go to Task 2 . If it is not, go to Step 5 .
5. The fault will be at IC201 (see Figure 15.1 ), since any fault with the
9 V 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 123 . If the repair failed or the fault could not be found, replace
the main-board assembly and go to “Final Tasks” on page 123 .
Task 2 —
3V Power Supply
If the 9V supply is correct, check the 3V DC supply ( +3
V
0
AN
) next.
1. Measure the voltage +3
V
0
AN
at the
TP
601 test point
(see Figure 15.1 ).
2. If the voltage is correct, go to Task 3 . If it is not, go to Step 3 .
3. The 3V regulator IC603 is suspect (see Figure 15.1 ). Check the
regulator as described in Task 3 of “Power Supply Fault Finding” on
page 132 .
pin 4 of IC201: 9.0
±
0.3V DC
TP601 test point: 2.9
±
0.3V DC