Accessories; Primary Voltage Circuit - Chamberlain LiftMaster Professional BG770 Installation And Maintenance Manual

2. Accessories

Add-on accessories can create many of the problems that are credited to the operator. Many
applications have more than one accessory item attached to the operator and some of these items
even draw their power from the operator.
Some of the symptoms that can show up because of accessories:
The operator won't close.
The operator won't open.
2A.
Whenever the problem is thought to be an accessory and there are more than one connected to
the operator, always disconnect one accessory at a time and then test the system. This will
hopefully isolate which item is causing the problem.
2B.
If an accessory item is being used as an access control device (used to open or close), falls in the
closed position or sends out a continuous signal. The operator will hold the gate in one position
until the signal from the accessory is removed.
2C.
In some applications, the gate may begin to move then either stop or stop and reverse within a
couple of seconds. This can be caused by an external obstruction device that has failed.
2D.
If there are many accessories attached to and powered by the operator, there may be too much
current draw for the operator's control transformer. This operator can only supply approximately 2
amps @ 24 vac. Double check all accessories for their current requirements.

3. Primary Voltage Circuit

Use extreme caution when troubleshooting the primary voltage circuit! There are five (5) items
in this circuit that could be causing trouble, and they are:
Motor
Transformer
3A.
The first thing to check is the incoming power. Is it there
at the incoming side of the power disconnect switch?
3B.
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.
The operator will not run.
The operator begins to run, then stops or reverses.
Contactor (see Figure 15)
Power Disconnect Switch
23
Troubleshooting
01-G0674F17
Figure 15
Doc 01-G0674
Rev D