ESAB PCM-875A Installation, Operation And Maintenance Manual page 90

SECTION 6
6.2.5 Air is On but nothing happens when torch is signaled to fire.
6-6
PCM-875A Plasmarc System
·
Check pilot arc fuse located on rear panel. If it is
open, nothing will happen when torch switch is
depressed.
·
Check torch. Make sure heat shield is very tight.
·
Check to assure high frequency is present at torch.
If not, then listen for high frequency at high frequency
generator. It is located on bottom/right side of the unit.
High frequency gap is set to .040". Disconnect HI
FREQUENCY leads. Check for 115 volt supply to high
frequency unit between P2-12 & P2-13 of control
board with torch switch closed.
·
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:
§
Check the operation of the Thermal Switch. See
D.3.a. above.
§
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)
§
Check air flow switch. There may be internal
short. See D.2.c above.
§
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 400 volt unit
If not, one of following could be malfunctioning:
§
Check the capacitors C1 and C2 for any
damage.
§
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.
§
Check Inrush current resistor, R10 and SCR1.
Both are located on the input bridge heat sink.
Replace it if malfunctioning.
§
IGBTs (2 on 230 V, and 1 on the 400 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.
Troubleshooting