458
c. To check if the output is shorted, measure the resistance by putting the ohmmeter leads across
the output. Put the black lead to the "work" terminal and the red lead to the torch electrode termi-
nal. The reading should be about 2K OHMs.
b. If the resistance reading is dierent than above, check the torch, the output bridge and Start-up
Board (PCB-6).
E. Air is On but nothing happens when torch switch is operated.
1. Check the torch. Make sure that the valve pin is installed and the heat shield is very tight.
2. Check to assure high frequency is present at the torch. Disconnect HI FREQUENCY leads. Check for
575 volt supply to the high frequency unit between P2A-1 & P2A-3 of the High Frequency Board (PCB2)
with torch switch closed.
3. With HI FREQUENCY leads disconnected, measure open circuit voltage. It should be 320 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 (TS1). 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 ow switch. There may be internal short. See D.2.c above.
d. Measure voltage across C5 or C6 capacitor. It should be as follows:
approx. 325 VDC with 230 V supplied to the 230/460 volt unit.
approx. 294 VDC with 208 V supplied to the 230/460 volt unit.
approx. 325 VDC with 460 V supplied to the 230/460 volt unit.
approx. 282 VDC with 400 V supplied to the 400 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 C5 and C6 for any damage.
2.) Check input bridge/SCR Module (BR1) This can be checked without taking it out of the cir-
cuit using an volt/ohmeter. Replace it if found malfunctioning. Follow bridge installation
instructions.
3.) Check Inrush current resistor (R1), located on the Input Bridge Heatsink and SCR (Q1). Re-
place if malfunctioning.
e. IGBTs 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.
SECTION 5 TROUBLESHOOTING
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