This page will offer no help for the common joystick or button. These are simple enough to just replace. This page offers help for the less common and more unique controls out there.
Spinners - look under Optical Encoder wheels or Potentiometers
Steering Wheels - look under Optical Encoder wheels or Potentiometers
Pedals - gas pedals are probably Potentiometers, while breaks and other pedals might simply be switches.
Flight yoke - look under Optical Encoder wheels or Potentiometers
This type of joystick is used by a select few games, such as Sinistar, Blaster, and Arch Rivals (Joust was first developed with these joysticks, but then changed to 2-way joysticks)
It is called 49-Way joystick because each direction (north, south, east, west) has 3 optos, with an opto being triggered for one of three positions in that direction (close, middle, furthest). So that's 3 in each of the 4 directions, so that's 12 righ t there. Then, if you move between two directions, can trigger one of three optos for one direction, and one of three optos in an adjacent direction. So that's 3 ways to chose 3, 3 x 3 = 9. Since there are 4 quadrants, that's 9 x 4 = 36. Add 12 + 36 + no opto's triggered (center), that's 49 ways the joystick can be positioned.
This picture will simplify things:
Imagine the joystick is centered at position 25, and you are able to move 3 positions in any direction.
The most common problem with this joystick is actually minor; there is a cross shaped rubber do-hickey which keeps the joystick centered (normally called "spider"). You can still find replacements for these. GroovyGameGear has these available under "modifications" section:GroovyGameGear. If you want a cheaper solution, take four short but thick rubber bands and loop them around the joystick shaft in place of the original rubber spider.
The benefit of this joystick is that you can imply both a direction and give WEIGHT to that direction. Typically for game play, that means the further you press the joystick in one direction, the faster your ship or player would move.
These joysticks are just strange. Fortunately, they were used in a limited number of games, with Escape from the Planet of Robot Monsters being the most common.
The joystick works based off the famous Hall-Effect...er...effect. Basically, there are some magnetics and some sensors which can detect how far the magnet has moved.
There really isn't much information on repairing these. Your only conselation is to know that they can be substituted by an analog joystick.
Analogy joysticks are nothing more than two potentiometers. See that section.
Potentiometers can be found in all sorts of controls, like Star Wars yokes, flight yokes, steering wheels, spinner knobs, joysticks, levers, and pedals.
These come in many different values, most of the time causing a voltage to range from 0VDC to +5VDC. So first, I would make sure the +5VDC is getting there in the first place if you are getting no response. Check connections as usual. If the movement o f the object is sparatic, I would invest in some "Tuner cleaner", which you can pick up at your local Radio Shack. Simply spray it on the pot in question, and it should clear up the problem. If not, go back to Radio Shack and see if they have the correc t value of potentiometer that you're looking for.
Trackballs are simply two encoder wheels whose axi's are spun by the rolling of a ball that is in contact with the axi's. If your trackball is being to "grind", then it's time to clean the roller pins, and possibly replace them.For other trackball parts, see ArcadeShop. They have everything for rebuilding these.
For Atari 4" trackballs such as found in Atari Football, Atari Basketball, and Missile Command, contact Mantis Amusements for the rollers. The bearings are standard R6 bearings that you can get online at McMaster-Carr, part #60355K14.
To rebuild one 4" trackball, you'll need 2 rollers and 5 bearings. It will be well worth it.
Optical encoder wheels are actually part of trackballs also, but this section is dedicated just to the spinner knobs.Atari Tempest/Major Havok
If your knob goes "BRRRRRrrr" when you spin it, simply add some 3-in-1 oil to the shaft and it will go away just like that.
If the movement of the object on the screen is not moving, or acting sparatic, more likely the problem is board related. The pokey chips on the board are suspect. If you are using a known good board, double check the connector between the wiring harness and the control panel. If you're SURE that it's the Tempest knob now, first try cleaning the opto's with alcohol and a Q-tip. If that doesn't work, the optos are probably bad.
From Rick Schieve:
Electronics (1-800-826-5432) had various optos cheap so I bought several kinds to try. Catalog #OSU-22 (H22A1) are single optos but using 2 of them in place of the Atari dual opto seems to work fine.
Omega Race (Bally Midway's only vector game) has it's own type of encoder wheel, which was later replaced by a more reliable 360 degree potentiometer. There are instructions on how to build one of your own online.