Lincoln Electric SVM138-A service manual Automatic Shutdown

B-9 B-9

OPERATION

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If such a grounding lead fault occurs, the meter will still be on and will be reading. The trigger circuit will not operate, however. To release the circuit, press the "GLP Reset" button. See Figure B.3 or B.4 for the location of this button.

The following precautions are recommended to avoid GLP shutdown:

•Do not allow the electrode to contact the case of the wire feeder or uninsulated part of its wire reel stand when the gun trigger is activated.

•Be sure that all work lead connections to the work make tight metal-to-metal electrical contact.

•Do not allow excess input cable or work cable to be placed closer than 3 feet to the wire feeder.

•Do not coil excess input cable assembly or use an uncoiled assembly as shipped from the factory. Instead, loop excess length back and forth in 3 to 6 foot straight lengths. Coiling the input cable results in a transformer action between the electrode conductor cable and ground lead in the multiconductor cable and the ground lead in the multiconductor control cable. This can cause current to flow in the ground lead, which will falsely activate the GLP.

AUTOMATIC SHUTDOWN

If the LN-9 GMA voltage control is unable to supply the SET value of arc voltage while welding, the automatic shutdown circuit will activate. This protection circuit immediately returns the LN-9 GMA control to idle state within a few seconds after the arc voltage discrepancy occurs.

Typical causes for the activation of this protective shut- down circuit are as follows:

a)SET value of arc voltage is outside the power source range.

b)Power source voltage control not set for REMOTE.

c)Misconnection of LN-9 control cable leads to power source.

d)Incorrect weld polarity connections, or settings, at the LN-9 GMA or the power source.

e)Lost connection of LN-9 GMA voltage sensing leads (#67 and #21) between the arc and voltage control, or a blown 1/8 amp fuse on the Voltage PC board.

In the case of full range control power sources, such as the DC-600, this protective shutdown circuit could pre- vent welding under the conditions of (c), (d), and (e) above by holding the power source output at minimum. The power source output might even be too low to establish an arc.

Although out of range shutdown can occur with all power sources when working with very low or very high arc voltages, it is most likely to occur when using the R3S models with somewhat limited voltage range of the various taps. For instance, if the R3S-400 triangle tap setting is for 31 volts, the range of control from the remote circuit is approximately 7 volts, i.e., 27-1/2 to 34-1/2 volts at nominal input voltage. If the LN-9 GMA controls are set for 29 volts and the input voltage to the R3S goes up, it may not be possible for the LN-9 GMA control circuit to hold the 29 volts. The welding will shut down. By changing to the 27 volt triangle setting, the range will be approximately 23-1/2 to 30-1/2 volts, and at high input voltage there will be sufficient control to hold the SET arc voltage.

The same general procedure can be used on other power sources. For example, if the LN-9 GMA keeps shutting down and the other possible causes have been checked, adjust the SET voltage higher and/or lower than the desired voltage. Then you can deter- mine what change in the range controls of the power source is required to supply the desired voltage.

In some cases, it is also possible to hold the ACTUAL button pressed while starting the arc. Before the LN-9 GMA shuts down, the actual arc voltage can be read on the digital meter. Comparing this reading to the SET reading will tell what change in the range controls of the power source is required to supply the desired volt- age. Should the meter read zero, check the connec- tions of LN-9 GMA sensing leads #21 and #67. Should the meter read a minus (-) voltage, the polarity con- nections or settings at the LN-9 GMA or power source are wrong.

LN-9 GMA Wire Feeder