Guardian Technologies 4760, 4456, 4390, 4389, 4759 Test 5 Wire Continuity, Test 6 Check Field Boost

SECTION 2.4

DIAGNOSTIC TESTS

PART 2

AC GENERATORS

8.Set the AUTO-OFF-MANUAL switch to MANUAL. Once the engine starts, record the AC voltage.

9.Set the AUTO-OFF-MANUAL switch to OFF. Reconnect Wire 11 and Wire 22.

RESULTS:

If CONTINUITY was NOT measured across each wire, repair or replace the wires as needed.

10.Set VOM to DC amperage.

11.Remove jumper lead connected to Wire 4 and Wire 15.

12.Connect one meter test lead to battery positive twelve- volt supply Wire 15, located at the 15A fuse. Connect the other meter test lead to Wire 4 (still disconnected from previous tests). Measure and record static rotor amp draw.

13.Set the AUTO-OFF-MANUAL switch to the MANUAL position. Once the engine starts, repeat step 12. Measure and record running rotor amp draw with the engine running.

14.Set the Auto-Off -Manual switch to OFF. Reconnect Wire 4 to the voltage regulator.

RESULTS:

Refer to Chart on Page 2.4-3: “Results - Fixed Excitation Test/Rotor Amp Draw Test.”.

TEST 5: WIRE CONTINUITY

DISCUSSION:

The voltage regulator receives unregulated alternating current from the stator excitation winding, via Wires 2, 6, and 162. It also receives voltage sensing from the stator AC power windings, via Wires 11 and 22. The regulator rectifies the AC from the excitation winding and based on the sensing signals, regulates the DC current flow to the rotor. The rectified and regulated current flow is delivered to the rotor brushes via Wires 4 (positive) and 0 (negative). This test will verify the integrity of Wires 0 and 162.

PROCEDURE:

1.Set VOM to its "R x 1" scale.

2.Remove Wire 0 from the voltage regulator, 4th terminal from the top. Also voltage regulator is labeled (-) next to terminal.

3.Connect one test lead to Wire 0, connect the other test lead to a clean frame ground. The meter should read

CONTINUITY.

4.Disconnect Wire 162 from the voltage regulator, 6th terminal from the top. Disconnect the other end of Wire 162 from the excitation circuit breaker. Connect one test lead to one end of Wire 162, and the other test lead to the other end of Wire 162. The meter should read CONTINUITY.

TEST 6 - CHECK FIELD BOOST

DISCUSSION:

See "Field Boost Circuit" on Page 2.2-1. Field boost current (from the circuit board) is available to the rotor only while the engine is cranking. Loss of field boost output to the rotor may or may not affect power winding AC output voltage. The following facts apply:

o A small amount of voltage must be induced into the DPE winding to turn the voltage regulator on.

oIf rotor residual magnetism is sufficient to induce a voltage into the DPE winding that is high enough to turn the voltage regulator on, regulator excitation current will be supplied even if field boost has failed. Normal AC output voltage will then be supplied.

oIf rotor residual magnetism has been lost or is not sufficient to turn the regulator on, and field boost has also been lost, excitation current will not be supplied to the rotor. Generator AC output voltage will then drop to zero or nearly zero.

PROCEDURE:

1.Locate Wire 4 that is routed from the circuit board and connects to the voltage regulator terminal, third from the top (see Figure 3). Disconnect that wire from the voltage regulator terminal.

2.Set a VOM to read DC volts. Disconnect Connector C2 from the control panel (C2 is the closest to the back panel).

3.Connect the positive (+) VOM test probe to the terminal end of disconnected Wire 4.

4.Connect the common (-) VOM test probe to the grounding lug.

5.Crank the engine while observing the VOM reading. While the engine is cranking, the VOM should read approximately 9-10 volts DC. When engine is not cranking, VOM should indicate "zero" volts (see Figure 4).

RESULTS:

1.If normal field boost voltage is indicated in Step 5, replace the voltage regulator.

2.If normal field boost voltage is NOT indicated in Step 5, check Wire 4 (between regulator and circuit board) for open or shorted condition. If wire is good, replace the circuit board.

Page 2.4-4