Troubleshooting - The Protector System™ (Infrared Sensor); Setting The Tension - Chamberlain LiftMaster Professional LM1000A Service Training Manual

Troubleshooting Infrared Sensor
1. In the event of the receiver LED indicator light not coming on after installation, check the
following:
• Power supply to the door opener.
• Short circuit in the black/white wire. This can occur under the cable terminals or
connection terminals.
• Incorrect wiring between the sensor and the door opener.
• Interruption of power circuit (broken circuit).
2. If the transmitter LED indicator light shines steadily but the receiver LED indicator light does
not, you must:
• See if an obstacle is in the way.
• Check the alignment.
• Check the connections.
(NOTE: CONSULT PAGES 28-30 FOR FURTHER INFORMATION ON INFRARED SENSOR
FAULT ANALYSIS).
Setting the Tension (Chain/Belt)
The correct adjustment of the tension, the chain or the belt is key to the service life of the motor.
Incorrect tensioning causes the motor bearing to wear prematurely.
Thread the spring nut on to the carriage screw until finger tight. Insert the tip of a screwdriver (1) into
one of the slots in the nut ring (2) and brace it firmly against the header sleeve. Fit an open-end spanner
(3) on the square head of the spring nut (4) and turn the spring nut by approx. 90° in a clockwise
direction until the nut ring (2) is released against the header sleeve (5). This sets the spring to the
optimum chain tension. If the chain is too loose, it can slip off the sprocket. If the chain does slip, re-
tighten the spring nut by turning the nut 180° in a clockwise direction.
The spring should not be pressed completely together.
It is normal for the chain or belt to sag somewhat when the door is UP (CLOSED), but this has
no effect on the service life of the opener.
FIGURE 17 C-rail
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