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F-34TROUBLESHOOTING & REPAIRF-34

STATIC SCR TEST (continued)

Figure F.5 - Plug J4 Location

G3909

Plug

J4

TEST

 

 

 

 

 

 

 

 

 

 

 

 

PROCEDURE

 

 

Removal and Replacement.

1.

Remove main supply power to the PRECI-

4.

Repeat Step #3 testing SCR2, SCR3 and

 

SION TIG 275 and remove the case top and

2.

left side.

5.

SCR4.

Locate and remove plug J4 from the control

To further check the SCRʼs functions, use an

3.

board. See Figure F.5.

 

SCR tester and proceed to the Active SCR

Using an analog ohmmeter, test the resis-

 

Test.

 

tance from anode to cathode of SCR1.

 

NOTE: Also check diode D1.

 

Reverse the meter leads and check from

6.

 

cathode to anode of SCR1. See Figure F.5. If

Replace plug J4 on the control board.

 

a low resistance is indicated in either direc-

7.

Replace the case top and left side.

 

tion, SCR1 is faulty. Replace the SCR Bridge

 

Assembly. See SCR Bridge Assembly

 

 

Figure F.6 - SCR TEST POINTS

LIFT BAIL STABILIZER

DIODE D1

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SCR4 CATHODE

 

SCR1 ANODE

SCR3 / SCR4 ANODE

SCR3 CATHODE

SCR1 / SCR2 CATHODE

SCR2 ANODE

 

PRECISION TIG 275

 

 

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Lincoln Electric SVM162-B service manual 34TROUBLESHOOTING & REPAIRF-34, Static SCR Test, Removal and Replacement