Tweco Hefty II CC CV Voltage Sensing Wire feeder - Manual (Page 35)

With input power supplied to the wire feeder, measure the DC voltage on the motor control
p.c. board from the right side of R12 (+) to the right side of R2 (-) (See Figure 5-2). While vary-
ing the wire feed speed knob from minimum to maximum, the voltage should change from ap-
proximately 0.25 to somewhere between 2.75 to 5.75 depending on the input voltage.
If not, replace the wire feed speed potentiometer (R1).
Replace the motor control p.c. board if necessary.
G. Wire feeds but no gas flows
Check to see if the gas cylinder is empty or the valve closed.
Make sure proper gas flow rate has been set.
Check for a possible restriction in the gas line or gas valve.
Check to see if the welding gun nozzle is plugged.
Check gas valve (L1), terminal strip (TB1), plug J1 on the 12 VDC driver p.c. board, and plug
J3 on the motor control p.c. board for loose or faulty connections.
With wires disconnected from the gas valve (L1), measure the resistance across the gas
valve terminals. The resistance should be between 15 to 30 ohms.
If not, replace the gas valve (L1).
An electronic protection circuit may have activated.
Reset by placing power switch in the off position for at least 60 seconds.
Replace the 12 VDC driver p.c. board if necessary.
H. Gas flows all the time or leaks
Make sure all connections are tight.
Check for foreign material inside the gas valve.
See Gas Valve Maintenance in the Maintenance chapter of this manual.
I. Wire feeds, contactor closes, but welding wire is not hot - there is no arc
Make sure all connections have been made to both the power source and wire feeder.
Make sure the cable between the contactor and feedhead is properly connected.
If using a CV power source, make sure the output contactor has been energized.
See “Prewelding Procedure” section in this manual.
Check to see if the contactor contacts are excessively worn.
Replace contactor assembly.
J. Wire feeds, contactor does not close, and welding wire is not hot - there is no
arc
Check contactor (K1), terminal strip (TB1), and plug J1 on the 12 VDC driver p.c. board for
loose or faulty connections.
With the contactor (K1) wires disconnected from the terminal strip (TB1), measure the resis-
tance of the contactor coil. The resistance should be between 3 to 6 ohms.
If not, replace the contactor (K1).
An electronic protection circuit may have activated.
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TROUBLESHOOTING
7-4 June 5, 2000 Revised