Garage Door Opener Schematic



Question:
Does someone have the schematic of the Craftsman Garage Door Opener model 139.5399011 (3/4 HP)? I am interested in the way the force is controlled. Thanks in advance.

Answer:
I don't have a copy of the schematic for your unit, but I do have one for the 139.53200 Craftsman openers I installed in our home about 20 years ago. From what I can see, the "up force" and "down force" controls are potentiometers used as rheostats to set the dc current fed into two pins of a control IC. There is also a photoelectric motor shaft "RPM Sensor" which feeds pulses into another pin on the same IC. The IC has two outputs which (through transistor buffering) energize the coils of two relays (UP and DOWN). Normally open contacts on those relays applies line voltage across one of two separate windings in the drive motor. The "other" motor winding gets a phase shifted voltage fed to it through a single capacitor connected between the "hot" ends of the two windings. The other ends of the windings are both tied to neutral. There's a third output from the IC which drives a relay controlling the light bulb on the front of the opener. The IC also has a pair of inputs for the "up limit" and "down limit" switches and a "Command" input from the radio receiver. There's also a "clock" input which gets a low voltage 60 Hz signal fed to it. So, I'll make an informed guess that the "force" adjustments control how much the motor speed is allowed to slow down before the IC decides it's time to call it quits and unpowers a relay to remove power from the motor.





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