Lincoln Electric 11519 Service Manual page 71

F-25
ACTIVE SCR RECTIFIER ASSEMBLY TEST (continued)
FIGURE F.7
LOCATION OF LEADS X2 AND X3
NEGATIVE
CAPACITOR
BANK BUSS
BAR
6. Disconnect leads X2 and X3 (braided copper
strap) from the negative capacitor bank buss
bar using a 1/2 in. open end wrench. See
Figure F.7.
7. Separate leads X2 and X3 from the negative
capacitor bank buss bar. Be sure there is no
electrical contact.
NOTE: DO NOT DISASSEMBLE THE SCR REC-
TIFIER HEAT SINK ASSEMBLY.
8. Use a commercial SCR tester or construct the
tester circuit shown in Figure F.8. One 6-volt
lantern battery can be used. R1 and R2 resistor
values are ±10%. Set voltmeter scale low, at
approximately 0-5 volts or 5-10 volts.
a. Test the voltage level of the battery. Short
leads (A) and (C). Close switch SW-1.
Battery voltage should be 4.5 volts or high-
er. If lower, replace the battery.
TROUBLESHOOTING AND REPAIR
LEADS X2 AND X3
CONNECTION
Power MIG® 255XT
FIGURE F.8
SCR TESTER CIRCUIT AND SCR CONNECTIONS
F-25