Tait TB7100, Service Manual

Page: 126 / 370

128 Power Supply Fault Finding TB7100 Service Manual
© Tait Electronics Limited October 2005
Task 1 —
Check Inputs to
SMPS
The test equipment and radio should be set up as described in “Test
Equipment Setup” on page 82 . If not already done, remove the main-board
assembly from the chassis. Connect the control head to the assembly. Then
check the SMPS as follows:
1. Use a multimeter to check the supply voltage at pin 7 of IC602
(see
Figure 9.1 ) in the SMPS circuitry; the voltage should be:
If it is, go to Step 5 . If it is not, go to Step 2 .
2. Disconnect the 13.8 V supply at the power connector PL100. Check
for continuity and shorts to ground in the path between the power
connector PL100 and pin 7 of IC602 (see
Figure 9.1 ). Locate and
repair the fault.
3. Reconnect the 13.8V supply. Confirm the removal of the fault by
measuring the voltage at pin 7 of IC602. If the voltage is correct,
continue with
Step 4 . If it is not, the repair failed; replace the main-
board assembly and go to “Final Tasks” on page 123 .
4. Press the
ON
/
OFF
key. If the radio powers up, return to “Initial Tasks”
on page 111 . If it does not, go to Step 5 .
5. Check the digital power-up signal at pin 5 of IC602
(see
Figure 9.1 ); the signal is active high, namely, when the voltage
exceeds 2.0 V DC. Measure the voltage at pin 5.
If it exceeds 2.0V, go to Task 2 . If it does not, go to Step 6 .
6. Keep the probe of the multimeter on pin 5 of IC602 and press the
ON
/
OFF
key. The voltage should exceed 2.0 V DC while the key is
depressed. If it does, go to Task 2 . If it does not, go to Step 7 .
7. Disconnect the 13.8 V supply at the power connector PL100. Check
for continuity and shorts to ground in the path from pin 5 of IC602,
via R600 and via Q709 in the interface circuitry (see
Figure 10.4 ), to
pin 9 of the control-head connector SK100 (
ITF PSU ON OFF
line).
Locate and repair the fault. Go to Step 8 .
8. Reconnect the 13.8 V supply. Press the
ON
/
OFF
key. If the radio powers
up, return to “Initial Tasks” on page 111 . If it does not, go to Step 9 .
9. With the probe of the multimeter on pin 5 of IC602 (see Figure 9.1 ),
press the
ON
/
OFF
key again. The voltage should exceed 2.0V DC
while the key is depressed. If it does, go to Task 2 . If it does not, the
repair failed; replace the main-board assembly and go to “Final Tasks”
on page 123 .
pin 7 of IC602: 13.8 V DC
pin 5 of IC602: more than 2.0 V DC