Tweco Troubleshooting Power Supply - Manual (Page 31)

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considered outside the supply. If it still sets code 2-7, 2-8 or 2-9 problem is inside
power supply or in user installed equipment.
Shorts outside the power supply
Reconnect the negative and/or pilot leads at the rear of the power supply. It’s
highly unlikely to have short between the negative (Torch) cable and the Pilot
cable or Work cable between the power supply and RAS. The only possibility is
if the insulation of the negative cable had worn or burnt so it contacts the table
(work) or if both negative and pilot cable have been worn or burnt and are
touching each other. Inspect the cable insulation for any place it may be worn or
burned through allowing contact with the table.
Most likely this short is in the arcstarter or the torch head or consumable parts.
• Inspect the torch consumables, make sure all parts are in place and are the
correct numbers and there is no foreign matter between them.
• Disconnect and insulate torch lead pilot wire in the RAS. The pilot wire
from the torch, not the cable that goes to the power supply. Disconnect
the RAS control cable from the RAS. Attempt to start torch. If still get
code 2-7 short is in RAS.
o Inspect for physical shorts, wires that have been disconnected or
broken, etc.
o Shorted capacitor on RAS Capacitor PCB. Measure for short from
NEG fast-on (spade) terminal to PLT terminal and to chassis.
• If do not get code 2-7 after disconnecting the pilot wire, the problem is in
the torch leads or torch head. Only place the pilot wire can contact the
negative in the torch leads is at the ends. You can easily inspect the RAS
end but have to remove the torch mounting tube to see the torch end
connections. If no shorts evident here replace the torch head. You can try
to measure for a short with a meter but shorts can be a carbon path that has
too much resistance to be detected with a meter but still carry current
when subjected to a couple hundred volts.
Shorts inside the power supply
For a short inside the power supply to cause current to be detected by the Pilot
or Work lead current sensors the short has to on the output side of the sensor and
shorted to something, such as the negative (Torch) terminal. Possibilities are:
o Blue wire from Work buss bar to CN2-1 on PCB8 (WK-5687).
Disconnect CN2 on PCB8, Apply CNC START. If no code 2-7
replace PCB8.
o Red wire from Pilot buss bar CN3 on PCB8 (WK-5687). Disconnect
CN3 on PCB8, Apply CNC START. If no code 2-7 replace PCB8.
o Black wire on Work buss bar, red wire from pilot buss bar and blue
wire from Negative buss bar go to J6 on CCM. Highly unlikely there
could be a short here but inspect the wires and look arcing on or under