Miller XMT 450 CC, Technical Manual, Page: 46 / 84

PRE-POWER CHECKS
TM-257 220 Page 42 XMT 450 CC/CV
10-6. Output Diodes D1, D2, D3, D4
255 763-A / 252 419-A
!
Read and follow safety
information in Section 10-1
before proceeding.
!
Wear an earth grounded
wrist strap when performing
pre-power and power off
checks. Remove wrist strap
before performing any
checks or procedures with
power applied to the ma-
chine.
Diodes D1, D2, D3, D4
D4
D3
D2
D1
Output diodes D1 through D4 are two terminal modules with two internal diodes. The screw terminals are the anode connection of each diode.
The cathode of each diode is connected to the base plate of the module.
1. Visually inspect D1 through D4 for damage. If there is visible evidence of damage such as smoke or debris, replace the defective part along
with any other diodes found to be defective using this procedure.
2. First check across weld output terminals using diode check with DMM. Look for diode drop of .1 to .3 VDC with leads connected as follows. If
measurement is correct proceed to next pre-power check. If measurement is incorrect perform step 3 to determine defective component.
Positive Meter Lead Negative Meter Lead
Negative Weld Output Terminal Positive Weld Output Terminal
3. Isolate diodes by disconnecting main transformer leads from terminals. Check with DMM set to diode test. Look for a diode drop of .1 to .3
VDC across each terminal.
Positive Meter Lead Negative Meter Lead
D1 Anode (Top Terminal) D1 Cathode (Base)
D1 Anode (Bottom Terminal) D1 Cathode (Base)
D2 Anode (Top Terminal) D2 Cathode (Base)
D2 Anode (Bottom Terminal) D2 Cathode (Base)
D3 Anode (Top Terminal) D3 Cathode (Base)
D3 Anode (Bottom Terminal) D3 Cathode (Base)
D4 Anode (Top Terminal) D4 Cathode (Base)
D4 Anode (Bottom Terminal) D4 Cathode (Base)