LiftMaster BG770 Industrial-Duty Single Arm Barrier Gate Operator - Manual (Page 15)

15
LOW VOLTAGE CIRCUIT
The first thing to check is the circuit breaker.
The secondary voltage must be between 22 and 30Vac. This
voltage can be checked at the circuit board at terminals 3 and 6.
The contactor coils receive 24Vac. To activate the motor in either
the open or close direction. There are two contactor coils (one for
open and one for close).
The limit switches are S.P.D.T. (single pole, double throw). These
limit switches tell the operator to shut off at either the full open or
full close position.
GENERAL REFERENCE INFORMATION
THE GATE
Double check the gate and its related hardware. Does the
gate move freely? Are there unprotected pinch points? If yes,
then correct.
WIRING DIAGRAM
Always reference the wiring diagram that was supplied with the
operator. Note that some of the accessory items may have their
own wiring diagram.
If you cannot correct the problem or if you feel you will require
technical assistance, contact your local distributor or dealer. If you
do not have a distributor or dealer, then contact us for technical
assistance. Please when calling for assistance, make sure you
have the gate operator model number, voltage, phase, horsepower
and a list of all accessories that are attached to the operator.
PRIMARY VOLTAGE CIRCUIT
Use extreme caution when troubleshooting the primary voltage
circuit! There are five (4) items in this circuit that could be
causing trouble, and they are:
• Motor
• Transformer
• Contactor (Figure 13)
• Power Disconnect Switch
The first thing to check is the incoming power. Is it there at the
incoming side of the power disconnect switch?
If there is power, then check for it at the transformer primary
terminals. If there is voltage at the switch and none at the
transformer, then you probably have a bad power disconnect and
it should be replaced. Check secondary output of transformer for
24Vac output.
If the first two check out okay, then manually disconnect the
operator from the gate. Very carefully, using a screwdriver with
an insulated handle, press down on the open side of the
contactor. Then do the same to the close side of the contactor.
Did the operator run in both directions? If it did, the problem may
be in the low voltage control circuit. It if did not, then the problem
is either in the contactor or the motor.
If the contactor is suspected to be causing the problem, first
carefully check all wiring connections at the contacts (Figure 13).
Disconnect Power! Using a volt-ohmmeter, take continuity
readings across the contacts of the contactor. Remove wires from
one side of the contactor. Place one probe on 1 and the other
on 2. You should get NO continuity; now press down on the
contactor; you should get a continuity reading. Repeat this on all
of the contactor’s contact points.
If the problem is thought to be the motor, it is recommended that
it be replaced. It is possible that the thermal overload inside the
motor has overheated. Wait approximately 15 minutes, then try
running unit.
NOTE: Some motors have the overload built into the motor itself,
while other units have a separate overload in the controller
(Model BG770 uses a manual reset overload).
T R O U B L E S H O O T I N G
Figure 13
Contactor