ESAB PCM-1125 Instruction Manual page 23

SECTION 5
should read a direct short. If not then it should read open.
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 trans-
former has exceeded preset limits.
a. To check if the output is shorted, measure the resistance by putting the ohmmeter leads (make sure to
disconnect 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
depressed.
2. Check the torch. Make sure that 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 to 0.040". 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 with 230 V supplied to the 208/230 volt unit.
approx. 294 VDC with 208 V supplied to the 208/230 volt unit
approx. 325 VDC with 460 V supplied to the 460 volt unit
approx. 400 VDC with 575 V supplied to 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. Re-
place it if malfunctioning.
e. IGBTs (2 on 230 V, and 1 on the 460 V & 575 V units) may be damaged. See IGBT installation procedure.
Before replacing IGBTs, make sure to check the zener diodes and pico fuses on the IGBT driver boards.
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TROUBLESHOOTING