Tait TP9100, Service Manual, Page: 270 / 326

270 CODEC and Audio Fault Finding
TP9100 Service Manual
© Tait Electronics Limited May 2005
12.1 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 149 . The remaining supplies that
need to be checked are:
■
Task 1: 7.5 V DC supply from battery via 0
Ω
link R950 (
7V5
LINK
)
■
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
)
One other supply used in the CODEC and audio circuitry is a 1.8 V DC
supply (
+1
V
8
) from the digital circuitry. Faults in this supply are dealt with
elsewhere.
Task 1 —
7.5V Power Supply
First check the 7.5V DC supply (
7
V
5
LINK
), which is required by IC200.
1. Remove the main board from the chassis.
2. Measure the voltage
7
V
5
SW
at pin 6 of IC200 (see Figure 12.1 ).
3. If the voltage is correct, go to Task 2 . If it is not, go to Step 4 .
4. The fault will be at IC200 (see Figure 12.1 ), since any fault with
7
V
5
LINK
in the interfaces circuitry will already have been rectified.
Therefore, check the soldering of IC200. Repair any fault.
5. Confirm the removal of the fault and go to “Final Tasks” on
page 134 . If the repair failed or the fault could not be found, replace
the main board and go to “Final Tasks” on page 134 .
Task 2 —
3V Power Supply
If the 7.5 V supply ( 7
V
5
LINK
) is correct, check the 3V DC supply ( +3
V
0
AN
)
next.
1. Measure the voltage +3
V
0
AN
at the
TP
3
V
0
AN
test point
(see Figure 12.2 ).
2. If the voltage is correct, go to Task 3 . If it is not, go to Step 3 .
3. The 3V regulator IC604 is suspect (see Figure 12.2 ). Check the
regulator as described in Task 4 of “Power Supply Fault Finding” on
page 156 .
pin 6 of IC200: 7.5V DC
TP 3V0 AN: 3.0
±
0.3V DC