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 13.8V 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 2.0V DC. Measure the voltage at pin 5.
If it exceeds 2.0V, go to Ta sk 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 2.0V DC while the key is
depressed. If it does, go to Task 2
. If it does not, go to Step 7.
7. Disconnect the 13.8V 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 13.8V 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
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