ESAB Powercut 875 Manuel D'instruction page 210

sectIon 5
b. If the switch is malfunctioning, replace it. Clean the surface of the heat sink before installing the switch.
4. over current. The fault light will be on continuously. This indicates that the input current to the main transformer
has exceeded preset limits.
a. To check if the output is shorted, measure the resistance by putting the ohmmeter leads (make sure to discon-
nect HI Frequency leads):"+" of the meter to Torch "+" output terminal and Work "-" lead of the meter to the "-"
output 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, the output bridge and Filter Board (PCB-5).
e. air is on but nothing happens when torch switch is operated.
1. Check the pilot arc fuse located on the rear panel. If it is open, nothing will happen when the torch switch is de-
pressed.
2. Check the torch. Make sure that the valve pin is installed and the heat shield is very tight.
3. Check to assure high frequency is present at the torch. If not, then listen for high frequency at the high frequency
generator. It is located on the bottom/right side of the unit. The high frequency gap is set between 0.028" to 0.031"
disconnect hI frequency leads. Check for 115 volt supply to the high frequency unit between P2-12 & P2-13 of
the control board with torch switch closed.
4. With HI FREQUENCY leads disconnected, measure open circuit voltage. It should be 275 VDC between "Work" and
"Torch" terminals. If it is not present then 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. (safety reasons)
c. Check air flow switch. There may be internal short. See D.2.c above.
d. 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 460 volt unit
approx. 410 VDC for the 575 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 and SCR1. Both are located on the input bridge heat sink. Replace it if
malfunctioning.
e. IGBTs (2 on 230 V, and 1 on the 460 V units) may be blown. See IGBT installation procedure. Before replacing IG-
BTs, make sure to check the zener diodes and pico fuses on the IGBT driver boards.
210
maIntenance