Return to Section TOC
Return to Master TOC
TROUBLESHOOTING & REPAIR
SCR REMOVAL AND REPLACEMENT (continued)
FIGURE F.28 – SCR DETAILS
Return to Section TOC
to Section TOC
Return to Master TOC
to Master TOC
SPECIAL INSTRUCTIONS
NOTE: Before disassembling the existing recti- fier, note toward which heat sink the outer metal ring of the power SCR is mounted. Also, note the positioning of the gate lead of the SCR. Failure to reinstall the new SCR in the same ori- entation as the original may result in subsequent damage to the new SCR and other components of the welder. See Figure F.28.
CAUTION
The unclamping and clamping procedure out- lined below is critical for the prevention of inter- nal SCR damage. Failure to follow this proce- dure may result in subsequent damage of the SCR. Handle all SCRs with care.
spring. IT IS RECOMMENDED THAT NEW HARDWARE, LEAF SPRING AND HOUSING BE USED FOR REASSEMBLY.
5.Remove the old SCR.
6.Clean the area on the heat sink around the SCR mounting surface, using a putty knife or similar tool. DO NOT SCRATCH THE SCR MOUNTING SURFACE.
7.Polish each heat sink’s mounting surface using NO. 000 fine steel wool. Wipe surface clean with a
8.Inspect the mounting surfaces of each new SCR.
a.Remove all burrs and wipe clean. Do not use steel wool or any abrasive cleanser on the SCR mounting surfaces.
Return
Return to Section TOC
Return
Return to Master TOC
PROCEDURE
1.Remove the main input supply power to the machine.
2.Perform the SCR/Diode Rectifier Assem- bly Removal procedure.
3.Using the 7/16” wrench, remove the NEGA- TIVE heat sink plate. Diode D4 pigtail will have to be removed from the positive heat sink plate. This will give access to the SCR clamping hardware. When reassembling, be sure all insulators are in place. The heat sink plate should be electrically insulated from the mounting
4.Alternately loosen nuts 1/2 turn each until heat sinks are loose. Remove nuts and leaf
9.Apply a thin (0.001” to 0.003”) layer of PEN- ETROX
a.Care must be used to prevent foreign material contamination of the SCR to heat sink junction.
10.Place the new SCR between the heat sinks. Be sure that the outer metal ring of the SCR is facing toward the same heat sink as the old SCR’s metal ring. Be sure that the roll pin of the heat sink engages the “hole” in the SCR. The SCR contact surfaces must sit flat against both heat sink surfaces.