Troubleshooting; General; Testing And Replacing Bridge Assembly Components - ESAB 653 cvcc Instruction Manual

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SECTION 6

6.1 General

WARNING

If the power source is operating improperly, the following troubleshooting information may be used to locate the source

of the trouble.

Check the problem against the symptoms in the following troubleshooting guide (Table 6-2.) The remedy for the prob-

lem may be quite simple. If the cause cannot be quickly located, open up the unit and perform a simple visual inspection

of all the components and wiring. Check for proper terminal connections, loose or burned wiring or components, blown

fuses, bulged or leaking capacitors, or any other sign of damage or discoloration.

6.2

Testing and Replacing Bridge Assembly Components

The SCRs used in the power source are devices which allow current to ﬂow in only one direction. The SCRs are designed

to provide long trouble-free operation; however, should a failure occur, they may require replacement.

A. Testing SCRs.

1. Remove top and right side panel from the power source.

2. Locate the main rectiﬁer assembly containing the SCRs.

3. Electrically isolate main bridge assembly by disconnecting resistor R5.

4. With the ohmmeter on RX1 scale, place the positive lead on the anode (end of SCR with screw threads) and the

negative lead on the cathode (positive output terminal on the front panel). The meter should read minimum of 20

meg ohms.

5. Reverse leads and check each SCR. All readings should again show high resistance. The SCRs are bad if they show

low resistance in either direction.

6. Check the gate circuit on the SCRs by installing a jumper from the gate lead to the anode of the SCR. The meter should

read less than 5 ohms. Remove the jumper from the gate. The meter reading should increase (30-50 ohms).

When replacing SCR's, make sure mounting surfaces are clean. Using Alcoa No. 2 EJC Electrical Joint Compound or an equivalent,

apply a thin coat to the SCR mounting surface and positively locate in place on the heatsinks. Place the clamp in position with the

bolts through the holes in the heatsinks and proceed as follows:

DISCONNECT PRIMARY POWER AT WALL SWITCH, OR CIRCUIT

BREAKER, BEFORE ATTEMPTING INSPECTION OR WORK INSIDE THE

POWER SOURCE.

IMPORTANT