Preventive Maintenance

D-3	MAINTENANCE	D-3

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1.Perform the following preventive maintenance procedures at least once every six months. It is good practice to keep a preventive maintenance record; a record tag attached to the machine works best.

2.Remove the machine wrap-around cover and per- form the input filter capacitor discharge procedure (detail at the beginning of this chapter).

OVERLOAD PROTECTION

The machine is electrically protected from producing high output currents. Should the output current exceed 340-360A, an electronic protection circuit will reduce the current (“Fold Back”) to approximately 150A. The machine will continue to produce this low current until the protection circuit is reset. Reset occurs when the output load is removed.

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3.Clean the inside of the machine with a low pres- sure airstream. Be sure to clean the following components thoroughly. See Figure D.2 for loca- tion of these components.

•Power Switch, Driver, Protection, and Control printed circuit boards

•Power Switch

•Main Transformer

•Input Rectifier

•Heat Sink Fins

•Input Filter Capacitors

•Output Terminals

4.Examine capacitors for leakage or oozing. Replace if needed.

5.Examine wrap-around cover for dents or break- age. Repair as needed. Cover must be kept in good condition to assure high voltage parts are protected and correct spacings are maintained.

6.Check electrical ground continuity. Using an ohm- meter, measure resistance between either output stud and an unpainted surface of the machine case. (See Figure D.2 for locations.) Meter read- ing should be 500,000 ohms or more. If meter reading is less than 500,000 ohms, check for electrical components that are not properly insu- lated from the case. Correct insulation if needed.

THERMAL PROTECTION

Thermostats protect the machine from excessive operating temperatures. Excessive temperatures may be caused by a lack of cooling air or operating the machine beyond the duty cycle and output rat- ing. If excessive operating temperature should occur, the thermostat will prevent output voltage or current. The meter will remain energized during this time.

PC BOARD REPLACEMENT

1.Handle PC Boards by edges only.

2.Store PC Boards only in the bags that disperse static charges.

3.Inspect PC Board for burned conductors or com- ponents. If damage is visible, inspect the machine wiring for grounds or shorts to avoid damaging a new PC Board.

4.If there is no visible damage to the PC Board, install a new PC Board and see if the problem is fixed. If the problem is fixed by the new board, reinstall the old board and see if the problem reoccurs. If the problem does not reoccur, check the wiring harness and plugs for loose connec- tions.

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7. Replace machine cover and screws.

V300-I