ESAB ESP-50 Instruction Manual page 231

sectIon 6
over current. The fault light will be on continuously. this indicates that the
3.
input current to the main transformer has exceeded preset limits.
a. To check if the output is shorted, remove the heat shield and nozzle from
the torch and measure the resistance by putting the ohmmeter lead "+" of
the meter to "+" output terminal and Work, "-" lead of the meter to the "-"
output torch terminal. Reading should be about 2 K Ohms. Reverse the
voltmeter leads, the resistance reading should be less than 1.5 K Ohms.
b. If the resistance reading is different than above, check the torch and output
bridge.
F. air is on but nothing happens when torch switch is operated.
1. check the torch. make sure that the heat shield is very tight.
2. any one of the following may not be working properly:
a. check the operation of the thermal switch. see d.3.a. above.
b. check air check switch operation. It might be stuck in on position. pilot
arc will not initiate if this switch is in the on position.
c. measure voltage across c1 or c2 capacitor. It should be as follows:
approx. 325 Vdc for the 208/230 volt unit.
approx. 280 Vdc to 325 Vdc for the 400 or 460 volt unit
If not, one of following could be malfunctioning:
1). check the capacitors c1 and c2 for any damage.
2.) check input bridge/scr module (Ibr) this can be checked
without taking it out of the circuit using an volt/ohmeter.
replace it if found malfunctioning. Follow bridge installation
instructions.
3.) check Inrush current resistor, r10, located on the input bridge
heat sink. replace it if malfunctioning.
d. IGbts (2 on 230 V, and 1 on the 400 V & 460 V units) may be blown. see
IGbt installation procedure. before replacing IGbts, make sure to check
the zener diodes and pico fuses on the IGbt driver boards.
G. pilot arc is on but main arc does not transfer.
1. make sure work clamp is connected to work material.
2. check the torch. replace consumables if necessary.
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troubleshootInG