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Check the resistance reading between 75 on the ter- minal strip and 211 on SW #2. The reading must be 10K ohms. No reading will indicate an open rheostat and a low reading will indicate a shorted or partially shorted rheostat; in either case, replace.
TOGGLE SWITCH CHECK
1.Turn off the machine power input. SW #1 has 115 volts across it when the input power is connected.
2.Isolate the switch to be tested by removing all con- necting leads.
3.Check to make sure the switch is making connec- tions with a V.O.M. meter. The meter should read zero resistance.
4.Put the ohmmeter on X1K scale and measure the resistance between the terminal and the case of the machine (touch a self tapping screw). Reading should be infinite.
5.If either step (3) or step (4) fails, replace the switch.
REMOTE CONTROL CHECK
Disconnect the remote field control and connect an ohmmeter across 75 and 76 and rotate the rheostat in the remote control. The resistance reading should go from zero to 10K ohms. Repeat with ohmmeter across 77 and 76 with same results. Connect ohmmeter across 75 and 77. The reading should be 10K ohms. A lower reading will indicate a shorted or partially short- ed rheostat. A very high reading will indicate an open rheostat. In either of the last two cases, replace the rheostat. Check for any physical damage.
CHECKING POWER RECTIFIER BRIDGE
CAUTION
ASSEMBLY
Precise evaluation of diodes or SCRs require laboratory equipment. If a bridge problem still exists after test, please call a Lincoln Field Service Shop.
Equipment Needed:
1.V.O.M. or ohmmeter for diodes
2.Circuit Diagram 1 for SCRs
DEVICE ISOLATION (See the instruction manual parts list for the exact location.)
Disconnect the following leads from the bridge, shown in Diagram 2:
1.Wiring harness gate leads (G1, G2, G3) from gate lead connector J4 on control P.C. Board
2.AC leads X1, X2, and X3 from the anodes of the SCRs and cathodes of the diodes.
3.The 200, 221, 222, and 223 leads from the Snubber P.C. Board.
4.Lead 220 that connects to the latching resistor (R3).
5.The cathode of each diode (4 total).
POWER DIODE TEST
1.Establish the polarity of the ohmmeter leads and set to the X10 scale.
2.Connect the ohmmeter positive led to anode and negative lead to the cathode.
3.Reverse the leads of the ohmmeter from Step 2.
4.A shorted diode will indicate zero or an equally low resistance in both directions. An open diode will have an infinite or high resistance in both directions; and a good diode will have a low resistance in Step 2 and a much higher resis- tance in Step 3.
POWER SILICON CONTROLLED RECTIFIER TEST
The SCR must be mounted in the heat sink when mak- ing this test.
1.Connect the ohmmeter (set to the X10 scale) leads to the anode and cathode.
2.Reverse the leads of the ohmmeter from Step 1.
3.A shorted SCR will indicate zero or an equally low resistance in one or both directions.
4.Establish the polarity of the ohmmeter. Connect the positive lead to the gate and the negative lead to the cathode.
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