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SECTION 6 – TROUBLESHOOTING
6-1. Troubleshooting Tables
A. Welding
Trouble
No weld output.
No or erratic weld output.
No or erratic DC weld output only.
Low or high weld output.
Miller Legend
Check fuse F1, and replace if necessary (see Section 8-6).
Check integrated rectifier SR2, and replace if necessary.
Check diode D4, and replace if necessary.
Clean slip rings, and install new brushes if necessary (see Section 6-15).
Disconnect leads 21, 23, and 33 from brushes, and check continuity across slip rings. Replace rotor
if necessary.
Check resistance and connections of resistors R2 and R4; R2 and R4 are each 12 ohms 10%. Re-
place resistor(s) if necessary. Adjust R2 and R4 according to Section 6-16.
Check resistance and connections of Fine Amperage Control R1; R1 is 0 to 30 ohms 10%. Replace
R1 if necessary (see Section 3-1).
Disconnect leads 22 and 29 from SCR/integrated rectifier SR2, and check for continuity between leads
22 and 29. Replace exciter stator if necessary.
For units with optional remote control, check capacitor C5 for a short or open, and check for proper con-
nections. Replace C5 if necessary.
Check voltage regulator board PC2 and connections, and replace if necessary (see Section 6-9).
Clean and tighten weld connections both inside and outside unit.
Check engine speed, and adjust if necessary (see Section 8-5).
Check to make sure Ampere Ranges switch S5 is not between positions. Check continuity of S5, and
replace if necessary.
Check reactor AC-Z for signs of winding failure. Check continuity across windings, and check for proper
connections. Replace AC-Z if necessary.
Check resistance and connections of Fine Amperage control R1; R1 is 0 to 30 ohms
R1 if necessary.
Disconnect leads 21, 23, and 33 from brushes, and check continuity across slip rings. Replace rotor
if necessary.
Check modular main rectifier SR1, and replace if necessary.
Check stabilizer DC-Z for signs of winding failure. Check continuity across windings, and check for
proper connections. Replace DC-Z if necessary.
Check engine speed, and adjust if necessary (see Section 8-5).
Adjust resistor R4 slider until 128 to 132 volts ac is obtained at 100 Hz receptacle RC4 (see Section
6-16).
Adjust resistor R2 slider until proper open-circuit-voltage is obtained at weld output terminals (see Sec-
tion 6-16).
Check resistance and connections of resistor R3 on suppressor R3, VR1 module; R3 is 1000 ohms
10%. Replace R3, VR1 module if necessary.
Check reactor AC-Z for signs of winding failure. Check continuity across windings, and check for proper
connections. Replace AC-Z if necessary.
See Sections 6-2 and 6-3 for test
points and values and Section 10
for parts location.
Remedy
10%. Replace
TM-428 Page 15
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Table of Contents
Troubleshooting
