Lincoln Electric Classic 300 MP Service Manual page 61

LINCOLN ELECTRIC
NOTE: This test must be performed with a good quality analog type ohmmeter. Many digital meters
will not provide stable or accurate resistance readings while the rotor is spinning.
This test requires that the brushes and slip rings are clean, in good condition and are properly
seated.
Perform the Exciter Brush And Slip Ring Service Procedure.
10. Insulate the lead wires that had been disconnected during the static rotor resistance test. Position
them so they cannot become damaged by the spinning rotor.
11. It is recommended that the ohmmeter leads be securely attached to the brush terminals, using clips
or terminals BEFORE starting the engine. See Figure F.25.
12. Start the engine and run it at high idle speed (1800 RPM). The resistance should read approximately
42 ohms* at 77° F. (25° C.)
13. Shut off engine and move one of the ohmmeter leads to a good clean chassis ground connection.
14. Restart the engine and run it at high idle speed (1800 RPM). The resistance should be very high, at
least 500,00 (500k) ohms.
15. If the resistance readings differ significantly from the values indicated, re-check the brushes and the
brush spring tension. If the brushes and slip rings are good, perform the Exciter Rotor Replacement
Procedure.
16. Securely connect the leads to the brush terminals (See Wiring Diagram) and replace the exciter
cover if testing and service is complete.
17. Using a 5/16" nutdriver, attach the four screws securing the exciter cover to the machine.
* NOTE: The resistance of the copper windings will change with temperature. Higher temperatures
will produce higher resistance and lower temperatures will produce lower resistance.
Figure F.24 – Exciter cover locations
Classic® 300 MP Service Manual
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