Tweco 400 XT Ultra-Cut Plasma Cutting System - Manual (Page 171)

ULTRA-CUT 400 XT
Manual 0-5275 APPENDIX A-�3
Troubleshooting:
1. If the fault is L2�0, applying START will clear the fault unless it becomes active again. An occasional problem may be due
to incoming voltage dips or sags (voltage drops lasting from ½ cycle to as much as a minute). Usually, if the plasma is
at fault, the problem will be present all the time. After ruling out everything else we may have to attach a monitor to the
power input to determine if this is the problem.
2. Voltage can be OK when not cutting or cutting at lower currents but at higher current too much voltage may be lost due
to undersize power cord or distribution wires.
a. Measure the voltage while cutting at higher current to determine if the drop is excessive.
b. Verify all power connections are clean and secure.
c. Verify correct wires size for the current draw per the recommendations in our manual as well as the local electrical
codes.
3. It is unlikely that an open connection on the J�1 jumper would result in a 2�0 fault, it is more likely to cause a Voltage
Mismatch fault. However, if it’s intermittent at exactly the right time, perhaps not fully plugged in, it possibly could show
up as 2�0. Check the jumper at J�1.
�. If the incoming voltage is OK and the problem persists it may be System Bias, CCM or connection between J�2 and J27.
a. If the incoming voltage is OK and D1�, ACV LOW, is on or the signal “AC V LOW b” on J�2-10 is “high” (about 2�VDC,
relative to TP1 or J�2-� ) the System Bias board is defective.
b. If D1� is not on and signal “AC V HIGH b” on J�2-10 is “low” (about 10-1�VDC, relative to TP1 or J�2-�) then System
Bias is OK and problem is in the CCM.
c. If J�2-10 is near zero volts there may be a bad connection between J�2-10 and J27-10 or J�2-7 and J27-7.
241-246 Inverter Section Input Voltage Error.
The System Bias board checks for input voltage high, low or missing a phase from the power coming in from the power cord.
It is unlikely but not impossible that a problem with the incoming power could result in 2�1-2�� codes. The 2�1-2�� codes
more likely point to problems with the power into or within a single inverter section or in the case of missing phase it may
be the contactor that supplies up to 3 inverter sections.
Once the input contactors close, applying voltage to the inverters, they test for input too high or too low and for missing
phase. When the input voltage is in the correct range, a green LED, D�, named READY, lights on the left side of the main
inverter board. If D� is not on, either the input voltage is out of range or the inverter is defective.
You can still get the 2�1-2�� code with a missing phase with the READY LED on. The LED will be going on and off rapidly
but appears to the eye to be on. In this case you can measure the signal on the ribbon cable. The signal previously called
READY is now called AC_INPUT_FLT. It is a differential signal on pins 1(+) & 2(-) of the inverters 30 pin ribbon cable. If the
AC input is correct you should read 5-�V between the pins. If AC_INPUT_FLT is true voltage on pins 1 & 2 will be less than 2V.
Some of the other faults such as Inverter Fault and Over Temperature also set the AC_INPUT_FLT (not Ready). However, they
will latch on associated LEDs or set different fault codes. In the event of an Input Voltage Fault the CCM does not remove
power from the inverter.
Things that can cause Input Voltage Fault codes:
1. Intermittently having the power drop out on one or more phases for at least 1 ms. a longer term loss would more likely
trigger a different fault. If it’s the incoming power it would be likely not always be the same inverter.
2. Phase missing or intermittent to a specific inverter the fault would always call out that inverter.
3. Intermittent connections on the fault signal internal to the inverter.
247-252 Inverter Fault
Once the input contactors close applying voltage to the inverters several tests are performed. The Inverter Fault signal latches
on so even if the cause has gone away you can see that there was a fault as indicated by red LED D1, INV FLT on the inverter
Control & Fault PCB. It is reset by applying start signal or cycling power. If the fault is still present it will come back on.