Thermal Arc ULTIMA 150, Service Manual

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SECTION 3: SERVICE TROUBLESHOOTING 22 Manual 0-2503
If the pilot light still does not come on, the prob-
lem is in the Logic PC Board. Disconnect the
primary power and place the Primary Power
ON/OFF Switch in the OFF position. Replace
the Logic PC Board.
NOTE
Shield Gas flows only when Pilot Arc ON/SET
Switch is in the ON position.
C. Pilot Arc demanded; momentary Pilot light on; no
pilot arc initiated.
When pilot is demanded, if pilot current hasn’t been
established within about 2 seconds, the pilot is in-
hibited until the PILOT ARC ON/SET Switch is
cycled off and on. This prevents the pilot from con-
tinuing to try to initiate a pilot into a damaged or
shorted torch. If the pilot light comes on for about 2
seconds and then goes off with no pilot arc estab-
lished, the control is working correctly, but something
is causing the pilot not to initiate.
a. Check for the presence of 300VDC at J14-3 to
J14-1, and at J14-7 to J14-5.
If this voltage is not above 240VDC, see the
procedure for checking the Main Diode and
Bridge Assembly in Section 3.14.
NOTE
When checking for the presence of the 300V, make
sure the measuring instrument is isolated from
GND because the 300V may be referenced to GND,
and connecting a GND referenced measuring in-
strument may cause a high energy short.
If 300VDC is present, the problem must be in
the torch or Pilot PC Board. Check the torch
for a shorted tip or other problems ( See the
appropriate torch Instruction Manual).
If the torch is OK, replace the Pilot PC Board.
D. Pilot Arc demanded; Pilot light on, pilot initiated
but erratic.
Erratic pilot can be caused by improper gas flow, air
leaks in the gas system, or pilot current adjusted too
low.
a. Check to make sure plasma and shield gas flow
rates and pilot current are within the accept-
able limits for the torch used. If not, correct
them.
b. Check for gas leaks as in Section 3.09.
c. If all settings are OK, and pilot is still erratic,
disconnect primary power and place the Pri-
mary Power ON/OFF Switch to OFF position
and replace Pilot PC Board.
Once the problem has been identified and corrected, make
sure the primary power is disconnected, and the Primary
Power ON/OFF Switch is in OFF position, then recon-
nect J3 to Logic PC Board to enable DC output circuit.
Repeat steps in Section 3.06, Basic Functions to ensure
the system is fully functional.
3.12 DC Pilot Indicator Light Status
After a pilot has been successfully established, the main
power converter can be turned on to provide weld power
by shorting TB1-3 to TB1-4 with a switch or other con-
tact. This should also cause the DC light to come on.
A. DC light does not come on when TB1-3 shorted to
TB1-4.
1. Faulty Pilot or Logic PC Board
a. Check to make sure the Pilot PC Board is not
inhibiting the main converter. Check this by
turning input off, disconnecting the ribbon
cable from J9 on Pilot PC Board, and turning
input on.
If DC light now comes on when requested, re-
place Pilot PC Board.
If DC light does not come on even with J9 rib-
bon cable disconnected, replace the Logic PC
Board.
B. DC light comes on but unit doesn’t weld.
1. Faulty Logic PC Board; Loose Connections
a. If pilot is OK and DC light comes on when re-
quested, check open circuit voltage. Do this
by depressing the voltage switch to volts mode.
This voltage should read approximately 50 to
60 VDC when the DC light is on and the arc is
not transferred to a work piece.
If the open circuit voltage is OK, and the unit
still will not weld, make sure the work lead
connection is solid and corrosion free.
If this voltage is low, but not 0, replace the Logic
PC Board.
If the open circuit voltage is 0, check the FET
Boards as in Section 3.14. If these check OK,
and all cables between FET Boards and Logic
PC Board check OK, replace the Logic PC
Board.