Lincoln Electric LF-72/74 service manual PC Board Troubleshooting Procedures

TOC

TOC

F-3	TROUBLESHOOTING & REPAIR	F-3
	PC BOARD TROUBLESHOOTING PROCEDURES

Return to Section

Return to Section TOC

Return to Master

Return to Master TOC

WARNING

ELECTRIC SHOCK can kill.

•Have an electrician install and service this equipment. Turn the input power OFF at the fuse box before working on equipment. Do not touch electrically hot parts.

CAUTION

Sometimes machine failures appear to be due to PC board failures. These problems can sometimes be traced to poor electrical connections. To avoid prob- lems when troubleshooting and replacing PC boards, please use the following procedure:

1.Determine to the best of your technical ability that the PC board is the most likely component causing the failure symptom.

2.Check for loose connections at the PC board to assure that the PC board is properly connected.

-Remove the PC board from the static-shielding bag and place it directly into the equipment. Don’t set the PC board on or near paper, plastic or cloth which could have a static charge. If the PC board can’t be installed immediately, put it back in the static-shield- ing bag.

-If the PC board uses protective shorting jumpers, don’t remove them until installation is complete.

-If you return a PC board to The Lincoln Electric Company for credit, it must be in the static-shielding bag. This will prevent further damage and allow prop- er failure analysis.

4.Test the machine to determine if the failure symptom has been corrected by the replacement PC board.

NOTE: It is desirable to have a spare (known good) PC board available for PC board troubleshooting.

NOTE: Allow the machine to heat up so that all electrical components can reach their operating temperature.

5.Remove the replacement PC board and substitute it with the original PC board to recreate the original problem.

TOC

TOC

3. If the problem persists, replace the suspect PC	a. If the original problem does not reappear by
board using standard practices to avoid static
	substituting the original board, then the PC
electrical damage and electrical shock. Read
	board was not the problem. Continue to look
the warning inside the static resistant bag and
	for bad connections in the control wiring
perform the following procedures:
	harness, junction blocks, and terminal strips.

PC board can be damaged by static electricity.

b. If the original problem is recreated by the

Return to Section

TOC

Return to Master

TOC

ATTENTION

Static-Sensitive

Devices

Handle only at

Static-Safe

Workstations

-Remove your body’s static charge before opening the static- shielding bag. Wear an anti-static wrist strap. For safety, use a 1 Meg ohm resistive cord connected to a grounded part of the equipment frame.

-If you don’t have a wrist strap, touch an un-painted, grounded, part of the equipment frame. Keep touching the frame to prevent static build-up. Be sure not to touch any electrically live parts at the same time.

substitution of the original board, then the PC board was the problem. Reinstall the replacement PC board and test the machine.

6.Always indicate that this procedure was followed when warranty reports are to be submitted.

NOTE: Following this procedure and writing on the warranty report, “INSTALLED AND SWITCHED PC BOARDS TO VERIFY PROBLEM,” will help avoid denial of legitimate PC board warranty claims.

Return to Section

Return to Master

-Tools which come in contact with the PC board must be either conductive, anti-static or static-dissipative.

LF-72/74