Paul wrote:
I have a ~20 year old Stanley model 3200 Garage Door Opener that
stopped working after I opened it using the remote. After that the door
would not close if the remote or the wall switch is pressed. The light
on the opener unit started blinking after 30 seconds or so. If the
open/close button on remote or wall is pressed again the blinking light
will stop for another brief period and you will hear a humming sound
from the motor as it is trying to operate but does not move anything.

The capacitor suggestion is a good one, but before checking it, unplug
the AC and discharge the capacitor properly -- see www.repairfaq.org.
While you're not supposed to do it, you can just short its 2 terminals
together with the shaft of a plastic handled screwdriver, but you
really should use a 5W, 10,000 ohm resistor first and then the
screwdriver. Those oil-filled capacitors can usually be tested
thoroughly with an ohm meter -- ohm reading will first be a short and
then slowly rise to several megaohms or even infinity. Electrical
supplies and hardware stores sell these capacitors.

Wiring connectors should be retightened occasionally because vibration
loosens them, and the wiring for the optical safety beam can break
right where it enters their cases.

The motor relays may have dirty contacts. There are 3 relays, each
housed in a small plastic cube. 1 is to run the motor in the forward
direction, another backwards, and the 3rd turns the overhead lamp on
and off. If changing the capacitor doesn't eliminate the buzz, you can
swap the lamp relay for the motor relays. Substitutes that will work
are widely available (even Radio Shack may have them), but mechanical
fit may be difficult without the exact same part (and possibly
dangerous -- must fasten relay well). Digi-Key, Allied, Newark are
some electronics supplies that carry a wide range of relays. The relay
contacts can't be fixed for long by cleaning them, even if you somehow
manage to remove the plastic cover.

Circuit boards take a beating from condensation and motor vibration,
and solder joints can crack. I believe your opener contains only 1
custom electronic component, a microprocessor (about 24 pins). The
most common failures on the board, other than the relays and solder
joints, are electrolytic capacitors, the voltage regulator, and the
transistors that drive the relays and their protective diodes (when one
of those diodes fails, the transistor goes as well).