ESAB PCM-875, Instruction Manual

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SECTION 5 TROUBLESHOOTING
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C. The Power light is on, but nothing happens when the torch switch is depressed. Fault light
does not activate.
NOTE: Unplug high frequency connection before attempting to work on this problem.
1. Check the Pilot Arc fuse (F2) located on the rear panel. An open fuse will indicate a short in the torch. If the fuse
is all right, then check the following:
a. With the machine power on, depress the torch switch. On the control board the LED 1 should be lit as long as
the switch is depressed. If not then check:
i. Turn power off to the machine. Unplug Control board. Put an ohmmeter across P5-1 and P5-2 to take
resistance reading. Depress torch switch. Meter should read a short. If not, then one of the following is
not working properly:
ii. Torch switch or the leads. Unplug the torch switch leads at the machine. Put a meter across the two plug
pins. Should read a short when the torch switch is depressed. If not, then either broken switch leads or
malfunctioning switch.
b. Check T2 transformer secondary voltages at the plugs P1 and P2. Refer to system schematic. Replace the
transformer if the correct secondary voltages are not present.
c. If everything above checks out all right, then the PCB1 Control Board should be replaced.
D. Fault light activates when torch switch is closed.
The Fault circuit is used to monitor conditions necessary for the safe operation of the PCM-875. The fault light
will glow amber under the following conditions and operations will come to a complete stop:
1. High/Low line voltage . The Fault Light will rapidly blink on and off (5 times per second). This indicates that
the input voltage is outside the “+” or “-” 15% safe operating range rating.
2. Flow fault - The fault light will be mostly on but will blink off for 1/10th of a second every second. This indicates
that the air flow is low.
a. Check the air pressure at the machine regulator. It should be adjusted to 65 psig. If no air pressure, check the
air at the supply point. Also, check for any obstructions in the air hose.
b. Air flow may be blocked at the torch tip. Check the torch consumables. Also check for any obstructions in the
torch leads.
NOTE: If above items check OK , the problem is internal. send unit to an Authorized Repair Station for repair.
c.. Put the ‘Air Check’ switch to On position. Air should flow through torch. If not, then the flow switch may be
stuck due to oil in the air. Clean air flow switch per supplier’s instructions or replace switch. To check if the
flow switch is open, put voltmeter leads between P1-12 and P1-1. It should read about 12 VDC. When the
flow switch closes, the voltage will drop to zero volts.
d. Air Check switch may also be malfunctioning if the air is flowing continuously or putting in the On position
does not turn air on.
3. Over Temperature. The fault light will be mostly off but will blink on for 1/10 of a second, every second. This
generally indicates that the duty cycle has been exceeded. Allow the power source to cool before returning to
operate.
a. Thermal switch may be open. It will open if the temperature at the IGBT base reaches 94oC. With the
machine power off, check the continuity between P1-1 and P1-2 of the control board. If the switch is OK, then