Protection PC Board
The protection PC Board is located on the back of the control box. It protects the PC Board from electrical noise. Most of the circuits on the Protection board are straight through connections. The board can be checked out in the field with a continuity tester or an ohmmeter. A copy of the
Snubber PC Board
The snubber PC Board is located on the main rectifier. Circuits on this board protect the SCR’s from high transient voltages. Failures on this board should be very rare. The only way to check the seven circuits on this board is to check each circuit, one at a time, using an ohmmeter, preferably an analog ohmmeter on the X10 scale. The first step is to connect one lead of the ohmmeter to the center plate of the rectifier assembly. This is the cathode connection for SCR’s 1 through 6. Next, disconnect the Snubber board lead that goes to the anode of SCR1. Connect the other ohmmeter lead to this snubber lead. The ohmmeter should show a low resistance initially, then swing towards high resistance if the snubber is good. Repeat this with SCR;’s 2 through 6, each time testing just one Snubber lead. Lastly, disconnect the snubber lead that goes to the cathode of SCR7, and perform the same test. The ohmmeter action should be the same for each SCR on the bridge.
Output Bypass PC Boards
One of these boards is mounted to each output terminal. Each board prevents high frequency energy and electrical noise from entering the
Control PC Board
This board, located inside the control box, is the heart of the machine. All welding output is controlled by this board. The Meter boards receive their information from the Control board as well. Very little external diagnostic work can be performed on this board.
If one control or function of the machine does not appear to be working, it is best to trace out the wiring associated with that function, switch or potentiometer all the way back to the Control board with an ohmmeter. If all check out there, verify that the following voltages are present at the output of the auxiliary transformer, T3.
Auxiliary Transformer (T3) | Plug P8 | Approximate |
Secondary Lead Color | Locations | Voltage |
|
|
|
Red to Red | 7 to 9 | 36V AC |
Red to White | 7 to 8 | 18V AC |
Yellow to Yellow | 1 to 2 | 10V AC |
Black to Black | 5 to 6 | 24V AC |
Orange to Orange | 3 to 4 | 18V AC |
|
|
|
Often, replacement with a known good board is the best service method. Remove the board that is suspected to be defective. Carefully look over the board, checking for burnt traces or components. If none are found, install the known good board. If the trouble goes away, reinstall the suspected bad board to confirm that the board was indeed at fault. If the problem is now gone with the original board installed, the problem is probably with one of the leads or connectors going to the board.
Meter PC Board
Both the Voltmeter and the Ammeter PC boards are identical. They both operate as display boards, displaying numbers sent to them by the Control PC board. The Meter boards do not make voltage or current measurements; the Control Board performs those functions.
If both meter boards are dark, (not lighted) chances are that either the secondary thermostat is open (see
“Thermostatic Protection” section), the auxiliary transformer T3 is defective (see “Control P.C. Board” section) or the Control board is defective.
If only one board is dark, make sure the machine is in a mode where both boards are supposed to light. There are certain modes where one board or the other is supposed to be dark. To check this, place the mode switch in the SMAW mode, and set the Output Control switch to “On”. Both meters should be lit. If one board is still dark, that board may be defective. The best way to check this is to switch the bad board with the other working Meter board right next to it. Replace the defective board.
CAUTION
If for any reason you do not understand the test procedures or are unable to perform the tests/repairs safely, contact your Local Lincoln Authorized Field Service Facility for technical troubleshooting assistance before you proceed.
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