Tweco Troubleshooting Power Supply - Manual (Page 30)

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• Short between power supply negative output and earth ground.
• Defective or incorrectly installed user supplied equipment such as torch
height controls that make connections to power supply output.
• Defective work current sensor.
• Defective PCB5
• Defective CCM
Troubleshooting Unwanted Current Faults (codes 2-7, 2-8, 2-9):
1. Code appears immediately following the power-on purge and before START is
applied then the fault is most likely a defect in the associated current sensor
circuit:
Code 2-8:
The pilot current sensor, HCT1, part of the Chopper module, gets + & - supply
voltage from the chopper. If the minus supply is missing the sensor becomes
unbalanced and will have an output that indicating pilot current even when there
is none. To troubleshoot, start by disconnecting harness from CN5 on chopper
PCB2, WK-5754. Turn power supply on and if code 2-8 does not appear fault is
in the chopper module. Check for any connectors loose or wires pulled out of
connectors on either of the chopper PCBs. If none found replace the chopper.
Look to descriptions for Current Sensors or PCB5 later in this section for more
details.
Code 2-9:
The work lead sensor, HCT2, gets +&- voltage supply and sends its output
signal to PCB5 via CN4. If the minus supply is missing the sensor becomes
unbalanced and will have an output that indicating work current even when there
is none. To troubleshoot, start by disconnecting CN4 from PCB5. If 2-9 code no
longer present at power up fault likely in sensor, it’s harness or PCB5. Look to
descriptions for Current Sensors or PCB5 later in this section for more details.
Code 2-7:
It is unlikely that code 2-7 will appear here but if it does follow steps for both
2-8 and 2-9.
2. Codes that do not appear until Start signal is applied are likely from an actual
current being detected during prefow when there should not be current.
First determine if problem is outside of power or inside. Code 2-9 disconnect
negative (Torch) or code 2-8 disconnect pilot cables from back of power supply.
For code 2-7 disconnect both. Disconnect control cable from J58 on the arcstarter
to prevent HF firing while troubleshooting.
In this condition unit will not pilot but upon applying CNC START system
should go through Preflow and attempt to turn on HF in arcstarter for 15 seconds
before setting code 1-2 because pilot did not start. HF will not turn on because
RHF control cable is removed.
If this happens, problem is outside the power supply. For Autocut units with
GCM 1000, even though the GCM 1000 is mounted on the power supply, it is