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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 DC-650 PRO wiring
diagram is needed also. All circuits should show
continuity, or nearly zero ohms resistance, from input
to output. Inputs and outputs can be identified by the
common lead number suffixes on the wires connected
to the Protection PC Board. For example, lead 75 on
the input side is common with lead 375A on the output
side. Lead 208 is common with 308, lead 209 is
common with 309 and 309A, etc.
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 DC-650 PRO.
Again, failures of these boards should be very rare.
The only way to inspect these boards is visually.
Inspect each board, looking for burnt traces or
components.
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 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.
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)
Secondary Lead Color
Red to Red
Red to White
Yellow to Yellow
Black to Black
Orange to Orange
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
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26
Plug P8
Approximate
Locations
Voltage
7 to 9
36V AC
7 to 8
18V AC
1 to 2
10V AC
5 to 6
24V AC
3 to 4
18V AC
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Table of Contents
Troubleshooting
