Sears garage Door Opener troubleshooting

My 20 year old Sears Craftsman 1/3 HP "single" garage door opener has suddenly become intermittent.
Sometimes the door goes up fine when activated by either the remote or the wall button, sometimes it goes up one quarter, sometimes half way and then stops, sometimes it will not go up at all, just jerks a couple of time as I push the remote, like it wants to, but then stops.
The door once in the up position will always go all the way back down again. The springs are fine as is the chain and door mechanisms. The wheels, track and chain are sufficiently greased.
The opener seems to work perfectly once or twice if the AC power cord has been pulled, and if one wants to open the door, plug the power cord in and activate the door.
I changed this start cap and the old one gets HOT (and ultimately the motor) after the door goes up and down a couple of times. I changed the cap back the the original cold cap, but the door motor just clicks. Any ideas or suggestions??
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snipped-for-privacy@email.mot.com wrote:

Hi, Points to the motor. 20 year old.....
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If you pull on the door to "help", would the opener work better?
If so, perhaps your garage door has gone out of balance.
With the opener disengaged, if your door is balanced, you should be able to open it manually without straining, and the door would hang half open if you leave it there.
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peter wrote:

Peter, Thanks for the reply. The door will manually lift easily and I will try to assist the lifting of the door when I energize the remote to see if that helps. The door when manually opened, will NOT stay in the half open position.
Thanks, Mike
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snipped-for-privacy@email.mot.com wrote:

Another possibility is the sensors. Do you have the sensor that shoots a beam across that when disrupted causes the door to stop? I have a fairly old opener too, and after much troubleshooting the same symptoms as yours, I found my beam/reflector were a little out of whack (probably got bumped). Anyway, straightened them out with each other and the jerking and intermittent activity cleared right up. Hope this helps,
js
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