ESAB ESP-150 Manuel D'instruction page 250

SECTION 5
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 each capacitor (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. A
shorted rectifier on D/R board can cause C25 capacitor to fail.
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 (675369) is defective.
d. Arc current is set too high.
e. Wrong cutting tip size. Use larger tip.
f. Defective current control board (675468 or 674940).
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 shorted.
b. Defective logic board (675369).
11. No or limited control of output current.
a. Defective current control potentiometer (CCP). Check by placing nega-
tive 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 (675369).
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 (675369).
B. SEQUENCE OF OPERATION (See Fig. 26)
1. Close primary disconnect switch.
a. Power supplied to unit.
2. Place Power Switch (ROS) to "Ready" position.
a. Fan motor (FM) and Pump motor on.
b. Low Gas LED on.
c. Control circuit energizes.
244
MAINTENANCE