Lincoln Electric WIRE-MATIC 255 SVM 119-A Service Manual page 72

F-21
WIRE DRIVE MOTOR AND TACHOMETER FEEDBACK TEST (CONTINUED)
4. Test for 2 - 25 VDC between lead
plug location 12J5 #539(B) (posi-
tive) (12J5) and lead #541(W)
(13J5) (negative) to determine if the
correct armature voltage is being
supplied. See Figure F.8.
a. Insert probes in to the Molex pin
cavities.
5. Pull the gun trigger.
6. Read meter.
from 2 - 25 VDC.
depending on wire feed speed.
a. If voltage to the wire drive motor
armature is zero, check the
wires between Plug J5 and the
wire drive motor. (Check J11,
J12, and J15).
Diagram.
b. If the wires are okay and voltage
to the drive motor armature is
zero, the Control Board may be
faulty. Replace.
c. If the correct DC armature volt-
age is present at the wire drive
motor, the motor or motor brush-
es may be faulty. Test and/or
replace.
d. If the motor is running at high
speed and the armature voltage
is high and uncontrollable, pro-
ceed with the tachometer test.
Test for Supply
Tachometer
1. Test for 15 VDC between lead
#515B (positive) (3J5) and lead
#206B (negative) (2J5) . See Figure
F.8 for pin locations.
a. Insert probes into Molex pin
cavities.
2. Pull gun trigger.
3. Read meter for 15 VDC.
TROUBLESHOOTING & REPAIR
Normal DC volts is
VDC varies
Test for Feedback Voltage to the
Control Board
1. Test for 1.5 - 3.5 VDC between lead
See Wiring
2. Pull gun trigger.
3. Read meter for 1.5 - 3.5 VDC.
NOTE: IF THE MOTOR IS NOT RUN-
NING, THE FEEDBACK VOLTAGE MAY
BE FROM 0 TO 5 VDC.
Voltage to
WIRE-MATIC 255
a. If the 15 VDC is present, check
the leads to the tach circuit.
b. If the leads are okay and 15
VDC is present, the correct volt-
age is being received from the
Control Board. Go to Feedback
Test.
c. If the 15 VDC is not present and
the leads are okay, the Control
Board may be faulty. Replace.
#555 (positive) (1J5) and lead
#206B (negative) (2J5) . See Figure
F.8 for pin locations.
a. Insert probes into Molex pin
cavities.
a. If the 1.5 - 3.5 VDC is present,
the tach circuit is sending the
correct feedback signal to the
Control Board.
b. If the 1.5 - 3.5 VDC is not pre-
sent or not correct, the Control
Board is not receiving the prop-
er feedback voltage from the
tach circuit. Check the leads
from the tach circuit to the
Control Board for loose or bro-
ken connections.
c. If the leads are okay, the Control
Board may be faulty. Replace.
F-21