Lincoln Electric IM481-B - Manual (Page 26)

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Procedure for Replacing PC Boards
When a PC board is suspected to be defective, the
following procedure must be followed:
1. Visually inspect the PC board. If the board has
fuses, check to see if any are blown. Are any of
the components damaged? Is a conductor on the
back side of the board damaged? If electrical dam-
age is visible on the PC board, inspect the
machine wiring for grounds or shorts to avoid
damaging a new PC board. Install a new PC board
only after a visual inspection of the PC board and
machine wiring is satisfactory.
2. If the problem is remedied by a new PC board,
install the old PC board and see if the problem still
exists. If the problem does not return with the old
board:
a. Check the PC board harness plug and PC
board plug for contamination, corrosion or
oversize.
b. Check leads in the harness for loose connec-
tions.
CONNECTING THE REMOTE CONTROL TO THE
MACHINE
Extreme caution must be observed when installing or
extending the wiring of a remote control. Improper
connection of this unit can lead to loss of control
and/or poor welding. Only the green lead can and
should be grounded to the machine case. When
extending the standard remote control, make sure the
leads are the same and the splice is waterproof. Be
very careful not to ground the cable when in use and
don’t let the lugs touch against the case.
OUTPUT VOLTAGE
The open circuit voltage of the machine should be
adjustable from 10 to 46 volts. If any other condition
exists, refer to the Troubleshooting Guide.
FAULT PROTECTION OPERATION
The overload protection circuit, in the Control Board,
will limit the welding current (heat) to approximately
550 amps if a short or overload is applied to the
machine.
CHECKING SNUBBER PC BOARD
In case of an SCR malfunction or failure, the Snubber
PC Board should be checked. Turn the machine off
and remove the sides of the machine. Board is mount-
ed on back of the case front.
1. Visually inspect the Board for overheated compo-
nents or damaged components.
CHECKING OUTPUT CONTROL RHEOSTAT ON
MACHINE
Turn machine off (“0” position).
Remove the screws from the hinged control panel and
open the panel.
Turn the Output Control switch to “Remote”.
Disconnect the harness plug from the Control PC
Board.
With an ohmmeter on X1K, connect it to lead 210 and
75 on R4.
Exercise caution to avoid damaging rheostat tabs.
Rotate the Output control rheostat. The resistance
reading should be from around zero to 10K ohms.
Check the resistance reading between 77 and 75 on
the terminal strip. The reading must be 10K ohms. No
reading will indicate an open rheostat and a low read-
ing will indicate a shorted or partially shorted rheostat;
in either case, replace.
POWER “ I/O “ SWITCH CHECK
1. Turn off the machine input power (“0” position). S1
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 open
and closed connections with a V.O.M. meter. Put
ohmmeter on X1 scale. The meter should read
zero resistance with switch “I” and infinite with
switch “0”.
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.
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.
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WARNING