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 3.3V DC supply (+3
V3) will already have been checked in
“Power Supply Fault Finding” on page 149. The remaining supplies that
need to be checked are:
■ Task 1: 7.5V DC supply from battery via 0Ω link R950 (7V5 LINK)
■ Task 2: 3V DC supply from 3V regulator (+3V0 AN)
■ Task 3: 2.5V DC supply from 2.5V regulator (+2V5 CDC)
One other supply used in the CODEC and audio circuitry is a 1.8 V DC
supply (+1
V8) 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 (7V5 LINK), which is required by IC200.
1. Remove the main board from the chassis.
2. Measure the voltage 7
V5 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
V5 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 7.5V supply (7V5 LINK) is correct, check the 3V DC supply (+3V0 AN)
next.
1. Measure the voltage +3
V0 AN at the TP3V0 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
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