TP9100 Service Manual Power Supply Fault Finding 149
© Tait Electronics Limited May 2005
8 Power Supply Fault Finding
Fault-Diagnosis
Tas ks
Fault diagnosis of the power-supply circuitry is divided into the following
tasks:
■ Task 1: initial checks
■ Ta s k 2: c h e c k + 3 V 3 S M PS
■ Ta s k 3: c h e c k + 1 V 5 S M PS
■ Task 4: check linear regulators
The regulators of concern in Task 4 are those for the 5V (2x), 3.0V, 2.5V,
and 1.8V supplies.
Tas k 1 —
Initial Checks
In order to power up the radio (processor running and display active) the
following supplies are required: +3V3, +1V8, and +1V5.
Set up the radio and the test equipment as described in “Test Equipment
Setup” on page 86. If not already done, remove the main board from the
chassis.
1. Use a multimeter to measure the 7.5V voltage across the battery pin:
2. While turning the power/volume control on, measure the voltage at
TP3V3 test point (see Figure 8.1):
If it is continuously 3.3V or turns on for a short time (approximately
2s), go to Step 3. If it never reaches 3.3V, go to Ta s k 2
.
3. While turning the power/volume control on, use a multimeter to
measure the voltage at C721 (see Figure 8.1). To do this, probe the
positive side of the C721 through the
DIG BOT can:
If it is continuously 1.8V or turns on for a short time (approximately
2s) go to Step 4. If it never reaches 1.8V go to Ta sk 4
.
4. While turning the power/volume control on, use a multimeter to
measure the voltage at
TP1V5 test point (see Figure 8.1).
If it never reaches 1.5V go to Ta sk 3
.
If it is continuously at 1.5V go to Step 5.
If it turns on for a short time (approximately 2s), go to Step 7.
(
TP3V3 and C721 should exhibit similar behavior.)
5. Ensure the programming cable is correctly connected, and use the
programming application to reload the radio’s programming file
voltage across BATT NEG and BATT POS: 7.5V DC
voltage at TP3V3: 3.3V DC ±5%
voltage at C721: 1.8V DC ±5%
voltage at TP1V5: 1.5V DC ±5%
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