Windup watches are more accurately called mechanical watches because they have a small spring-loaded mechanism, or movement, inside the case to regulate the watch. They are relatively easy to fix as long as you leave movement alone. The watch dial, hands, crystal and strap or bracelet are replaceable, but only an experienced watchmaker with the proper tools can repair the movement. Movements usually stop working because they get dirty. Try not to open the case unless it's absolutely necessary.
Locate the bezel on the front of the watch. It's a thin ring that holds the crystal, which is the plastic or glass that covers the dial. Bezels are easy to remove because mechanical watches are usually vintage. With your fingertips, twist the bezel counterclockwise until it's free from the case. The crystal should fall out.
Run your fingernail over the crystal. Replace it with a new one if the scratches have deep grooves. Dab some Brasso on the crystal if the scratches are light. Use a soft cloth to rub the paste into the crystal in a circular motion for at least five minutes.
Wipe away the paste and buff the crystal to a shine. Place the crystal inside the bezel and place it on the case. Rotate the bezel clockwise until it's tightened on the case.
Remove the crystal as instructed in Step 1 of the scratched crystal section. Place the feet of the hands grabber/remover tool directly over the hands post in the middle of the dial. Use the grabber to individually remove the hour, minute and second hands.
Use a cotton swab dampened in mild soapy warm water and gently clean the dial since you have the hands removed. Allow to air dry.
Replace all three hands so they remain identical. Return the hands grabber/remover to the now naked post and insert each hand in the order of their removal onto the post. Place the hands at 12 o'clock. Replace the crystal according to the instructions in Step 3 of the scratched crystal section.
Insert a case blade between the snap-down case and caseback of a windup watch and push down until the caseback pops from the case. You want to access the movement to repair or replace a broken stem or crown.
Place the watch face down on a clean table. Use a precision watchmaker's screwdriver to remove the screw closest to the stem and the edge of the case. The stem is attached to the crown, which is the small knob on the case edge at 3 o'clock. Unscrew the screw, and slide the stem and crown from the case.
Use needle-nose pliers to remove the stem from the crown. You will want to keep the original crown because it more than likely has the watch name engraved on it. Screw in with your fingertips the new stem into the crown. Tighten the stem with the pliers. Insert the stem into the hole at 3 o'clock. Return the screw to its hole to keep the stem in place. Tighten the screw.
Replacing the stem and crown is an easy task, but otherwise resist opening the case to avoid getting dirt on the movement.
Never remove a part by force. You will break it.