ESAB ESP-150 Manual De Instrucciones página 198

SecTION 5
7. No pilot arc - pilot arc contactor (Pac) drops out when main contactor (Mc) activates at end of 2-second
preflow.
a . Check for low open circuit voltage . It should be around 370 V at nominal line voltage .
b . Check voltage between each side of resistor R29 and the WORK output connection when MC is activated .
Place negative meter lead on side of resistor being checked and positive meter lead on the WORK output
connection . The voltage on one side should be the open circuit voltage (370 V) . The voltage on other side
should be above 175 V . If lower voltage is under 175 V, PAC will drop out .
c . Check the resistance of R29 . It should be 133 K ohm .
d . Disconnect R-29 resistor and measure the resistance from P1-1 to shunt (common) . Resistance should be
200 K to 250 K ohms .
e . Check for continuity between R29 and electrode (-) torch connections .
f . With power off, mechanically pull in PAC . The resistance between POS and WORK connections should be
8 ohms .
8. Main arc fails to transfer to work.
a . Make sure that work clamp is securely fastened to the work piece .
b . Check for proper function of pilot arc (PT-26) and high frequency unit .
c . Check main disconnect switch and fuses .
d . Check main contactor (MC) by disconnecting primary power and check each contact for closure using an
ohmmeter while physically pulling contactor .
e . Check C24 and C24A capacitors (1900 uf, 450 V) with an ohmmeter . Resistance should be 900-1000 ohms
with capacitor connected in the circuit . If shorted, replace capacitor . Then check R18 resistor . The resistance
of R18 should be 5 ohms . The resistance between "DRB POS" and "CAP (+)" should be 25 ohms . If the stud
mounted rectifier on D/R board is shorted, the 25 ohm will be less than 5 ohms even when meter probes
are reversed .
f . Check open circuit voltage . It should be about 370 volts .
g . Check F1 and F2 fuses . The open circuit can still be 370 volts with one blown fuse .
h . Current control board (674935) may be defective .
9. Short tip life.
a . Check for correct gas pressure .
b . Check gas flow rate using flowmeter (P/N 19765) .
c . Check to see if pilot arc contactor (PAC) remains activated after main arc transfers . This can be done by
observing the spark in the spark gap of the high freq . unit . The high freq . spark should shut off as soon as
main arc starts . If spark continues after main arc is established, either main contactor (MC) or logic board
is defective .
d . Arc current is set too high .
e . Wrong cutting tip size . Use larger tip .
f . Defective current control board .
10. Pilot arc cycles on and off when torch switch is not depressed.
a . Unplug torch switch plug . If cycling stops, then torch switch wires or plug or torch switch itself are short-
ed .
b . Defective logic board .
11. No or limited control of output current.
a . Defective current control potentiometer (CCP) . Check by placing negative meter lead on WORK output
connection and positive meter lead on current control board P1-2 . (P1 is the larger of the two plugs .) With
the fan running (machine at idle), adjust CCP from min . to max . They read zero at min . (1 .1 volts on ESP-
150); 10 Volts DC at max . The meter should move smoothly from zero to 10 V as CCP is rotated from min .
to max .
b . Defective logic board .
12. gas does not shut off after 10 seconds of preflow.
a . Turn off ready-off switch (ROS) . If gas continues to flow, solenoid valve is defective .
b . Defective logic board .
13. No arc.
Check that the mains power supply switch isturned on .Check that the welding current supply andreturn cables
are correctly connected .Check that the correct current value is set .
14. The welding current is interrupted during welding.
Check whether the thermal overload tripshave operated (indicated by the lamp on thefront panel) .Check the
mains power supply fuses .
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