Lincoln Electric SVM133-B service manual Troubleshooting and Repair

F-56

TROUBLESHOOTING AND REPAIR

F-56

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FINE CONTROL POTENTIOMETER TEST (continued)

TEST PROCEDURE

approximately 5.00 VDC in the maximum posi-

Section

Master

NOTE: In this test procedure, the positive output

tion. Also, the display on the control

panel

should steadily increase from 50-575.

stud is used for common.

to

to

4. If step 2 or 3 fails, turn off the machine. At J8

Return

Return

1.

Put the LOCAL/REMOTE switch in the “LOCAL”

Using the 5/16” nut driver, open the control panel

pins 5,8, & 9, perform a resistance check of the

and tilt out. Remove the control board cover.

fine control potentiometer (the control poten-

position. Set the range switch to the general fab-

tiometer is a 10K ohm potentiometer).

See

Figure F.27. Also, check continuity of all fine con-

rication tap. Start the machine.

trol potentiometer leads and LOCAL/REMOTE

switch. If any of the leads, switch or poten-

WARNING

tiometer fails the resistance check, replace the

faulty component.

There

are

high

voltages present

5. If the leads, switch and potentiometer pass the

inside

the

control box while the

resistance check, disconnect the J8

from the

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machine is running. THE VOLTAGES

control board and start the machine. Check the

ARE HIGH ENOUGH TO KILL. Use

voltage from J8 pin 9 to common. The voltage

Section

Master

extreme caution to avoid the back-

should be approximately 5.11 VDC. Check the

side of the receptacles, breakers, and

voltage from J8 pin 5 to common. The voltage

terminal strip while checking voltages inside the

should be approximately -.049 VDC.

If either

to

to

control box.

voltage check fails, replace the PC board.

Return

Return

2.

With the control potentiometer in the minimum

6.

Repeat steps 2-4 with the LOCAL/REMOTE

switch in the “REMOTE” position and a remote

position, check the voltage at the control board

control potentiometer hooked up to either

from J8 pin 8 to common.

Voltage should be

amphenol. When doing any continuity checks,

approximately -.025 VDC.

be sure to include the RF bypass PC board and

3. Slowly turn the control potentiometer CW. The

associated leads.

voltage should

steadily increase from approxi- 7.

When the test is complete, replace the control

mately -.025 VDC in the minimum position to

board cover and close the control panel.

TOCSectionto	TOCMasterto			Figure F.27 Control Board Plug J8 location
Return	Return						Pin #5
				C112
						Pin #8	Pin #9
					J20	J22
TOC	TOC						Plug J8
SectiontoReturn	MastertoReturn	J2				J1
		J6	J5	J8	J7
						J4
						COMMANDER 400