My garage door opener is acting in a peculiar manner. It sometimes will stop after the door is partially up or down and every couple of days refuses to work in the morning, but by the evening it is functioning again. I assume the motor is dying, but perhaps it simply needs some adjustment to the up and down force controls. When it is not working at all it is completely dead, even the light will not come on and it will not work with either the wall mounted switch or the remote. Any things for me to test or try?
Sounds like a cracked cold solder joint or some other mechanically loose connection. Vibration from the mechanism running might be causing the connection to break and thermal expansion can cause similar effects, which would explain the total lack of power. I’d get in there and pull apart any connectors and clean the contacts and if the problem persists, then reflow all the solder joints on any terminals and on the circuit board(s).
Get some spray lube/grease and apply it thouroughly in the roller tracks and on the rollers. If the track is dry and the door does not move smoothly enough unrestricted the opener will stop/reverse etc. every time it feels resistance.
It’s probably not the motor, or you’d still get the light. It could possibly be some thing to do with the sensors. If the rails are moving around (and if they’re mounted on the rails), that could cause the problem. To test that out, try blocking them and opening the door. If the light flashes, you know it’s not that. If the whole thing stops dead in it’s tracks and the unit is unresponsive, it’s a possibility.
Another real quick check is the power cord. Make sure it’s plugged in all the way. Over the years, the vibration may cause it to wriggle it’s way out of the outlet. If it’s just barely making a connection it could cause the symptoms.
Yes, and don’t forget the track of the opener itself.
Further guesses:
Does it ever start when you haven’t touched the remote? If so, change the code.
Does the door hang straight while moving? A broken spring will make it run crooked and bind up.
Do you catch a glimpse of a ghostly chicken when the door misbehaves? That’s a poultrygeist, and I can’t help you with that. 
It very well could be the motor starting capacitor. This will cause the motor to work intermittently. Depending on the age of your opener, the capacitor is prone to failure.
Take the cover off of your opener, locate the capacitor (a cylinder slightly larger than a “D” size cell that has two terminals on one end). A failed capacitor will probably have a noticable bulge or crack, and may have leaked or sprayed gooey electrolytic fluid around the inside of the unit.
You should be able to find a replacement at any business that services garage door openers, or even a good hardware store. The ratings (found on the side of the capacitor) are standardized, and are based on the horsepower rating of your opener. If a capacitor from another manufacturer is rated the same, it will work just as well (assuming it fits in the same spot physically).
This is something you can replace yourself, if you’re comfortable with tools.
Neither this:
nor this:
nor this:
will explain this:
I had one of my garage door openers (Stanley 1/2-hp) fail this fall, due to a faulty capacitor. The symptom was intermittent operation, and finally a failure to operate at all. At the end, when the opener switch was pressed, neither the light nor the motor would come on; the light didn’t even go into the “error” blinking mode. I suspect the circuit that controls the light is triggered by the operation of the motor. I replaced the failed capacitor, and it worked normally again.
All garage door openers might not work exactly the same as yours.
For the sake of argument, we’ll say that’s the case. But, the purpose of the start cap is to, well, start the motor. Once the motor is running, the start cap is no longer necessary and even if it failed entirely at that point, the motor will continue to run until switched off. Based on the OP, it’s very unlikely to be that since he says sometimes it will stop partway through the opening or closing cycle
Most of the time, when a motor start cap fails, you’ll hear a slight humming sound as the circuitry tries to energize the motor windings. It’s possible it’s a motor with a start/run cap, but the normal failure mode with these is usually either complete failure or markedly slow running speed, rather than intermittent normal operation. And they’re not terribly common on garage door openers. I’m not saying it’s impossible but it’s unlikely, based on the OP.
It is safe to fool with a capacitor if you’re not used to repairing electrical equipment? I thought capacitors could store a pretty harmful shock of electricity. I have always understood that that is why you should never open your TV or air conditioner.
Agreed; I missed the part of the OP about the door stopping while partially open.
Don’t attempt this if you’re not comfortable working with electrical components. You can, however, remove the opener cover and inspect the capacitor for physical signs of damage, at relatively little risk.
Mine was acting whacked out and I ended up replacing the remote (new batteries did zero). Worked fine after that.
Our garage door was acting weird. It worked intermittently, went up by itself, would stop half way up. Then all of a sudden it would work fine followed by fits of non-operation.
We discovered it was a loose wire on the “safety beam” boxes at the bottom of the door tracks. Tightened up the connection. garage door fixed.