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TROUBLESHOOTING & REPAIR
SCR REMOVAL AND REPLACEMENT (continued)
FIGURE F.20 – SCR DETAILSReturn to Section TOC
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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.20.
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.
5.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.
6.Polish each heat sink’s mounting surface using NO. 000 fine steel wool. Wipe surface clean with a
7.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.
8.Apply a thin (0.001” to 0.003”) layer of PEN- ETROX
PROCEDURE | a. Care must be used to prevent foreign |
| material contamination of the SCR to |
| heat sink junction. |
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1.Remove the main input supply power to the machine.
2.Perform the SCR/Diode Rectifier Assembly Removal and Replacement pro- cedure.
3.Alternately loosen nuts 1/2 turn each until heat sinks are loose. Remove nuts and leaf spring. IT IS RECOMMENDED THAT NEW HARDWARE, LEAF SPRING AND HOUSING BE USED FOR REASSEMBLY.
4.Remove the old SCR.
9.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.
IDEALARC
