User guide

TM-428 Page 15 Miller Legend
SECTION 6 – TROUBLESHOOTING
6-1. Troubleshooting Tables
A. Welding
. See Sections 6-2 and 6-3 for test
points and values and Section 10
for
parts location.
Trouble Remedy
No weld output. 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).
No or erratic weld output. 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 ± 10%. Replace
R1 if necessary.
Disconnect leads 21, 23, and 33 from brushes, and check continuity across slip rings. Replace rotor
if necessary.
No or erratic DC weld output only . 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.
Low or high weld output. 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.