Lincoln Electric IM409 IDEALARC R3R-400 - Manual (Page 20)

D-8 TROUBLESHOOTING D-8
TROUBLESHOOTING
PROCEDURES
PROCEDURE FOR REPLACING P.C.
BOARD
(The P.C. Board is located behind the front control
panel. Remove the nameplate screws to loosen the
control panel.)
When the P.C. Board is to be replaced, follow this pro-
cedure:
Visually inspect P.C. Board in question. Are any of
the components damaged? Is a conductor on the
back side of the board damaged?
1. If there is no damage to the P.C. Board, insert a
new one and see if this remedies the problem. If
the problem is remedied, re-insert the old P.C.
Board and see if the problem still exists with the
old P.C. Board.
a. If the problem does not exist with the old
board, check the harness plug and P.C.
Board plug for corrosion, contamination, or
oversize.
b. Check leads in the harness for loose connec-
tions.
2. If there is damage to the P.C. Board, refer to the
Troubleshooting Guide.
OUTPUT VOLTAGE
The open circuit voltage of the machine should be 67
to 71 volts and should not vary when the rheostat is
varied. If any other condition exists, refer to the
Troubleshooting Guide.
OVERLOAD PROTECTION
All IDEALARC® R3R, -300, -400, -500s have built-in
protective thermostats. If the rectifier or transformer
reaches the maximum safe operating temperature
because of frequent overload or high room tempera-
ture plus overload, the line contactor drops out stop-
ping the welder. The thermostats automatically reset
and the line contactor pulls in when the temperature
reaches a safe operating level.
The power rectifier bridge is also protected against
short term, high current overloads generally caused by
poor operating techniques.
For example, if an arc gouging carbon or the electrode
is allowed to touch – or almost touch – the work for a
couple of seconds or more, the overload protection
P.C. Board automatically reduces the output to mini-
mum and keeps it there until the overload is removed
or the machine is turned off.
CHECKING SNUBBER CIRCUIT
In case of an SCR malfunction or failure, the snubber
assembly should be checked. Turn the machine off
and disconnect one lead of the snubber assembly.
(Either 221, 222, or 223 depending on the SCR in
question. See wiring diagram.) The sides of the
machine have to be removed to do this. (See parts list
for the exact location.)
1. Visually inspect the snubber assembly for overheat-
ed components.
2. Using a V.O.M meter on the X10 scale connect the
positive lead to the lead removed. Touch the nega-
tive lead to the shunt. The indicating needle on the
meter will move quickly to the right (low resistance
value) and then slowly return to the left (high resis-
tance value). This indicates that the capacitor in the
snubber circuit is taking a charge.
3. If the needle stays to the right, the capacitor is
shorted and the assembly is defective.
4. If the needle does not move, the capacitor or resis-
tor on the snubber assembly is open and the
assembly is defective.
CHECKING CURRENT CONTROL
RHEOSTAT ON MACHINE
Turn the machine off.
Remove the control panel screws and open the front
cover.
Turn the current control switch to remote.
Disconnect the harness plug from the control board.
Put current range switch to “B” range.
With an ohmmeter on X1K, connect it to lead 210 and
211 on SW #2.
Rotate the current control rheostat. The resistance
reading should be from around zero to 10K ohms.
Check the resistance reading between 75 on the ter-
minal strip and 211 on SW #2. The reading must be
10K ohms.
IDEALARC® R3R, -300, -400, -500