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 TM5-4120-347-14
b. Inspect.
(1) Check that solder connections and terminals are tight and in good condition.
(2) Check that harness wires have no cuts, broken wires or frayed insulation.
(3) Inspect attaching hardware to be sure it is tight and in good condition.
(4) Inspect electrical parts for obvious damage such as cracks, evidence of overheating and broken
terminals.
(5) Replace all damaged or broken parts.
c. Test.
(1) Transformer T1/Resistor R1.
(a) Tag and disconnect leads and check for continuity across the primary winding and then across the
secondary winding. If either winding is open, replace the transformer.
(b) Check for shorts between one terminal and transformer case and also between one primary
terminal and one secondary terminal using an insulation tester, megger or multimeter on high ohms setting.
Replace transformer if a short is indicated.
(c) Apply 115 volts AC, 120 watts, to terminals 1 and 2 (input terminals). Voltage at transformer
terminals 3 and 4 should be 28 to 30 volts AC, 4 amps. Remove power from transformer. Replace defective
transformer.
(2) Rectifier CR1. Apply 28-30 volts AC to rectifier terminals 1 and 3. Output at terminals 4 and 2 should be
26 to 30 volts DC. Terminal 4 is negative, 2 is positive. Replace faulty rectifier.
(3) Capacitors.
(a) Disconnect the positive (+) lead of the capacitor from the circuit.
(b) Using an ohmmeter set to read high resistance, place the positive (+) probe on the disconnected
capacitor lead. Place the negative (--) probe of the ohmmeter on the negative lead of the capacitor or on a
common ground while watching the ohmmeter needle.
(c) The ohmmeter needle should move rapidly to a point about 2 to 3-3/4 up the scale, then slowly drop
back. If the needle does not move, the capacitor contains an open circuit and must be replaced. If the needle
moves quickly to the top of the scale and remains there, the capacitor contains a short circuit and must be
replaced.
NOTE
The ohmmeter test does not show the behavior of a capacitor under load. Such testing requires
special equipment which is not economically practical for testing small capacitors. If breakdown
under load is suspected, replace the capacitor.
d. Remove/Install.
(1) Transformer.
(a) Tag and disconnect wire leads.
(b) Remove tie down strap and resistor.
(c) Remove the four screws and lock washers and pull the transformer from the unit.
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