I am having problems with a Sears 1/2hp garage door opener model 139.53636srt. To close it you have to hold the inside control button in until it closes all the way. I replaced the sensors, and they are both lit and appear to work fine. I also checked all control and sensor wiring for faults and correct installation. The green led on the lift unit blinks 4 times and pause, repeat. The door will not close by remote, breaking the beam with the door open will not turn on the light, and one push of the control button will not close the door. Any ideas on what I should do next? I have a really big hammer...