Miller XMT 450 CC, Technical Manual, Page: 48 / 84

TM-257 220 Page 44 XMT 450 CC/CV
10-9. Troubleshooting Table
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Before connecting welding equipment to input (primary) power for servicing, be sure the input-power circuit protection is correct
for the welding equipment. Connect equipment to a dedicated circuit sized and fused for the rated output and duty cycle of the
welding equipment you are servicing. See the Electrical Service Guide section in this manual and National Electrical Code (NEC)
article 630, Electric Welders.
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Remove earth grounded wrist strap before performing any checks or procedures with power applied to the machine.
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Equipment serviced may need to meet additional requirements as specified in IEC60974-4, Arc Welding Equipment − Part 4: Periodic
Inspection and Testing.
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See Section 10-11 or 10-13 for test points and values and Section 13 for parts location.
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Use MILLER Testing Booklet (Part No. 150 853) when servicing this unit.
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See the MILLER Extranet for service memos that may aid in the repair of this product.
Trouble Remedy
No weld output; unit completely
inoperative. Place line disconnect switch in On position (see Section 4-8).
Check and replace line fuse(s), if necessary, or reset circuit breaker (see Section 4-8).
Check for proper input and output connections.
Check continuity of power switch S1, and replace if necessary.
Check control transformer T2 for signs of winding failure. Check continuity across windings, and
check for proper connections. Check secondary voltages. Replace T2 if necessary.
No weld output; meter display On. See Section 10-10 for HELP screens.
Unit overheated and HELP 3 or HELP 5 screen is displayed. Allow unit to cool with fans On (see
Section 10-10).
Check, repair, or replace remote control.
Check coil voltage and connections of contactor W1. Check continuity of coil and condition of
contacts. Replace W1 if necessary.
Check input and output voltages of hall device HD1. Replace HD1 if necessary.
Check output diodes D1 thru D4, and replace if necessary.
Check input rectifier SR1, and replace if necessary.
Check IGBT modules PM1 or PM2, and replace if necessary.
Check control board PC1 and connections, and replace if necessary (see Section 10-13).
Low weld output with no control. Check control board PC1 and connections, and replace if necessary (see Section 10-13).
Check front panel display board PC3 and connections, and replace if necessary (see Section 10-18).
Maximum weld output with no control. Check input and output voltages of hall device HD1. Replace HD1 if necessary.
Check voltage sensing leads from output terminals to front panel display board PC3 connections, and
replace if necessary (see Section 10-11).
Check control board PC1 and connections, and replace if necessary (see Section 10-13).
Check front panel display board PC3 and connections, and replace if necessary (see Section 10-18).
Limited output and low open-circuit
voltage. Check incoming power for correct voltage. Replace line fuse(s), if necessary, or reset circuit breaker
(see Section 4-8).
Check for proper input and output connections.
Check control board PC1 and connections, and replace if necessary (see Section 10-13).
Check front panel display board PC3 and connections, and replace if necessary (see Section 10-18).
Check IGBT modules PM1 or PM2, and replace if necessary.
Clean and tighten all weld connections.