Tweco 400 Ultra-Cut(May 2014) - Manual (Page 196)

ULTRA-CUT 100 XT/200 XT/300 XT/400 XT
A-68 APPENDIX Manual 0-5302
207 Unexpected Current in the Work Lead.
HCT1, a Hall Effect current sensor on the positive (work buss bar) measures the work lead current. Inverter section 1A is
enabled during preflow time but there should be no current in the work lead before the pilot is ignited and before the arc is
transferred to the work. If current greater than 8A is detected before or during preflow something is wrong.
1. 207 code before START applied:
• Defective work current sensor, HCT1.
• Defective Relay PCB
• Defective CCM
Defective Sensor
• The work current sensor, HCT1, receives power, +15VDC and -15VDC from the Relay PCB. Both must be present for
the sensor to work properly. Measure between Relay PCB TP1 (or J1-4) to J1-1 for +15VDC and to J1-2 for -15VDC.
• If either + or – 15VDC not present remove the J1 connector and repeat the measurement at J1-1 & 2 on the Relay
board. If the voltage is now present the sensor is defective or shorted (the harness may be shorted). If voltages still
not present, the Relay board is defective.
Relay PCB
• Relay board LED D12, Work Current Detected, will light if the current sensor signal exceeds 0.05V. If D12 is on, mea-
sure the sensor output signal at J1-3 with signal common on J1-1. This signal should be 0V +/- 0.04VDC. If greater
than +/- 0.04VDC with no work lead current, the sensor is defective. If the signal voltage is within the limits and D12
is on, then the Relay board is defective.
• If D12 is not on and the 207 code is still active, either the Relay board or the CCM is defective.
CCM or ribbon cable
• The work current signal leaving the relay board is on the 40 pin ribbon cable (Relay J4 to CCM J23) pins 27 (-) & 28
(+). If the voltage here exceeds 0.1VDC with no work current the Relay board is likely defective. Another possibility
is in the 40 pin ribbon cable either pin 27 or 28 is shorted to an adjacent pin. Otherwise the CCM is defective.
2. 207 code after START applied (during preflow):
• Short between power supply negative output and Work circuit.
• 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.
Shorts are more likely to cause DC output voltage low (code 205). However, if the short has enough resistance it is possible
to show code 207. To test, remove negative output cable and reapply Start. If 207 code does not appear problem is a short
somewhere outside the power supply.
User Installed Equipment
For user installed equipment to cause 207 code it would have to be connected on the output (to the rear) of the current
sensors. To test, disconnect user equipment and apply CNC START. If code 207 is gone user equipment was defective or
connected incorrectly.
208 Unexpected current in Pilot Circuit
The Pilot board includes a current sensor to measure the pilot current. There should not be any pilot current until the invert-
ers and the pilot board are enabled and the arc starter has fired to ignite the pilot. Pilot current or the signal indicating pilot
current should not be present until the arc starter has fired.
Unwanted current signal due to defective sensor or defective circuit boards will most likely be present as soon as the power
up sequence completes and will be indicated as an active fault, E208. An actual short allowing real current to flow in the pilot
circuit will not occur until the inverter and pilot board are enabled near the end of preflow. This will result in the inverters
immediately being shut off and displaying a “last” or “latched” fault, L208. An LED, D2, on the Pilot board lights when the
Pilot Board is enabled.