Control Board - Lincoln Electric SVM188-A Service Manual

E-3
FIGURE E.2 - FIRING BOARD,CONTROL BOARD AND RECTIFICATION
CONTROL POWER
TRANSFORMER
SWITCH
115VAC
•
Pilot
Light
w
CR2
•
Secondary
Thermostat
Primary
Theromstat
1CR Coil
CONTACTOR
CR1
FIRING CIRCUIT, CONTROL CIR-
CUIT AND RECTIFICATION
RECTIFICATION
The "neutrals" of the welding secondary windings in the
main transformer are connected together, and the six
starts are connected to the six Silicon Controlled
Rectifier (SCR) assemblies to form a six-phase output.
This six-phase AC output from the main transformer
secondary is rectified and controlled by the SCR
bridge.
FIRING BOARD
The firing board is powered by the three-phase 32vac
transformer windings. Each phase provides two firing
pulses, one for each of the two SCRs controlled by that
phase. When a gate firing enable
received, the firing circuit supplies the proper amount
of energy to the gates of the power SCRs. When this
gate firing signal is applied at the correct time, the SCR
will turn ON. The amount of ON time versus OFF time
determines the output of the machine.
Operation. At the same time the latching resistor is
connected across the machine's output circuit. The
latching resistor provides a pre-load for the SCR bridge
so the SCR's will stay activated providing open circuit
voltage (OCV).
THEORY OF OPERATION
FAULT PROTECTION
32VAC
32VAC
32VAC
14-pin
115VAC
Amphenol Receptacle
T • 115VAC
S
E
T
R
R
M
I
I
P
N
A
2
L
42VAC
115VAC
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
*
(trigger) signal is
See SCR
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
DC-600
OUTPUT
CONTROL SIGNAL
FIRING
BOARD
S
G
I
A
Fan G
T
Motor N
E
A
L
CONTROL
OUTPUT
TERMINAL
SWITCH
SHUNT
LATCHING
RESISTOR
SCR BRIDGE
CHOKE

CONTROL BOARD

The control board receives current feedback informa-
tion from the shunt and voltage feedback information
from the choke and welding output terminals. This
feedback information is processed on the control
board. The control board compares the commands of
the mode switch, the output control potentiometer (or
remote control device) and the arc force control with
the feedback information and sends the appropriate
output control signal to the firing board. In the event of
a "fault condition," the control board de-activates the
fault relay (CR2). See Protective Devices and Shut
Down Circuits.
An output choke is connected between the neutral con-
nection of the main transformer secondaries and the
negative output terminal. This large inductor stores
energy, and provides current filtering for the welding
output of the DC-600.
*
Triggering is accomplished by a connection of lead
#2 & #4 by way of the Output Terminal Switch or by a
remote signal from a wire feeder. The 2 to 4 closure
is indicated by LED10 on the firing Board and LED 6
on the Control Board.
TERMINAL
STRIP 1
OUTPUT
CONTROL
SWITCH
OUTPUT
CONTROL
BOARD MODE
SWITCH
F
E
E
D
B
A
C
POSITIVE
K
TERMINAL
F
E
E
D
B
A
C NEGATIVE
TERMINAL
K
E-3