Tweco 400 XT Ultra-Cut Plasma Cutting System With Automated Gas Control - Manual (Page 175)

ULTRA-CUT 400 XT
Manual 0-5306 APPENDIX A-51
Either Arc Starter
5. /RAS ON signal not on. CCM sends active low signal “ /RAS ON” over the 40 pin ribbon cable on pin 16 to the Relay &
Interface board. On the relay board RAS Control relay (K2) closes (RF ON LED, D23 on) sending 120 VAC to J8-3 with
return on J8-11. From here it either goes to the HF transformer T2 (AC200XT) or to J59 as described above.
a. Measure the signal “/RAS ON” on pin 16 of the 40 pin ribbon cable relative to TP1 on either the CCM I/O board or the
Relay board. If it is low (less than 1V) skip to step 6. Otherwise continue this step.
NOTE
If the CCM thinks there is already a pilot it would not enable the HF. Pilot board has a current sensor that sends a
differential analog pilot current level signal to the Relay board which in turn passes that signal to the CCM. On the
Relay board D11 LED “Pilot Current Detected” or just “PILOT” lights if it sees a signal from the pilot board.
Reasons why RAS Control relay would not close:
6. Pilot current flowing. There actually is pilot current flowing somewhere. Unlikely as it would normally set the 208 fault
but we have to rule it out.
a. Disconnect J41 on the Pilot board, if HF still doesn’t fire and the Relay board Pilot LED, D11, is still on, it’s due
to a fault in the detection circuits.
7. Faulty detection circuit. There isn’t any pilot current but a fault in the circuits measuring pilot current is indicating there
is current.
a. Measure between pins 8 (-) and 9 (+) on the Pilot ribbon cable from Relay board J3 to Pilot board J42. If there is
no pilot current it should be zero. Anything else indicates the Pilot board current sensor is faulty causing the Relay
board D11 to be on. Replace the Pilot board assembly.
b. If the Pilot current signal on the pilot ribbon cable was zero, measure between pins 23 (-) and 25 (+) on the 40 pin
ribbon cable between the Relay board and the CCM. This would also normally be zero if there is no pilot current.
Anything else would indicate the Relay board is faulty.