176 Diagnosis of Faults on Main Board TM8100 Mobile Radio Service Manual
May 2004 © Tait Electronics Limited
Task 3 —
Check Linear
Regulators
This section gives the general procedure for checking any linear
regulator. There are two possible faults: either the regulator has failed
and prevents the radio from powering up, or the regulator voltage is
incorrect. (The regulator IC might or might not have been removed
during earlier checks.)
1. Disconnect the 13.8 V supply. Check for continuity and shorts to
ground (if not already done) on the input, output and control line
of the relevant regulator IC. Repair any fault.
2. If the regulator IC has been removed, resolder it in position.
3. Reconnect the 13.8 V supply and press the
ON/OFF key. If the radio
powers up or the correct regulator voltage is restored, return to
Subsection 8.1. If the repair failed, go to Step 4.
4. Disconnect the 13.8 V supply. Replace the regulator IC with a
spare. Reconnect the 13.8 V supply and press the
ON/OFF key. If
the radio powers up or the correct regulator voltage is restored,
return to Subsection 8.1. If the repair failed, return to
Subsection 8.1 and replace the complete main-board assembly.
Figure 9.3 Regulator ICs under the CDC BOT can
LO2 BOT CAN
CAN FOR
DIGITAL
BOARD
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