158 Power Supply Fault Finding TM9100 Service Manual© Tait Electronics Limited August 2005Task 3 —Check LinearRegulatorsThis task describes the general procedure for checking any linear regulator.There are two possible faults: either the regulator has failed and prevents theradio from powering up, or the regulator voltage is incorrect. (The regulatorIC might or might not have been removed during earlier checks.)1. Disconnect the 13.8 V supply. Check for continuity and shorts toground (if not already done) on the input, output and control line ofthe 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 radiopowers up or the correct regulator voltage is restored, return to“Initial Tasks” on page 139. 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 radiopowers up or the correct regulator voltage is restored, go to “FinalTasks” on page 147. If the repair failed, replace the main-boardassembly and go to “Final Tasks” on page 147.Figure 7.3 Power-supply circuitry under the CDC BOT can, including 3V regulator IC603 and 2.5Vregulator IC604LO2 BOT CANCAN FORDIGITALBOARDTP601
