The Trak-Ball and Optical Sensor FAQ V2.0 (8-11-98) by: Gregg Woodcock Thanks to: Gary Ransom John Robertson Rick Schieve Ray Ghanbari Patrick Peters There are 3 basic sizes of Trak-Balls; "Mini" (used in games such as Centipede and in all cocktail cabinets), "Midi" (used in games such as Marble Madness and Millipede) and "Maxi" (used in games such as Missile Command and "Xs and Os" Football). They are all the same except for the varying sizes of the balls and shafts. The Mini and Midi consist of 1 ball, 1 idler shaft, 2 roller shafts, 2 encoder wheels, 2 radial optical coupler PCBs, and 6 ball-bearing assemblies. The Maxi is a little different in that the idler shaft is replaced by a short rod acting as an axel for one ball-bearing assembly (so there is a total of only 5 for the Maxi ball). The ball rides on top of this bearing assembly which spins around the rod (which is the opposite of the other two points of contact where the ball rides on top of the rods which spin inside the bearing assemblies). Missile Command (and other?) cocktail and cabaret controllers (even though they are Mini) use this same no-idler-shaft design. Generally I have found that if the case of the controller is plastic, it has an idler roller; if it is metal, it does not. Also, while electrically compatible, there are more components on the opto boards for the Maxi balls. The worst is that the idlers and the bearing assemblies are unique for the Maxi and are hard to come by. Luckily the shafts are easily machined (Rick Schieve generally has plenty of "home-brew" shafts available). As far as the bearing assemblies go, you should exchange the idler bearing assembly with one of the bearing assemblies from one of the roller shafts. The idler one is always very beat up around the ball contact area and since the ball does not touch this part at all on the shafts' bearing assemblies, they are always in perfect shape (and it doesn't matter if they're not after the swap). The Mini Trak-Ball is 2-1/4" diameter which is the exact size of a standard billiard ("pool") ball. Replacing the standard cue ball with some other ball is simple and amusing (even down right disturbing) to see. The Midi Trak-Ball is 3" in diameter. The roller and idler shafts are longer and have a larger diameter in the Midi and those in the Maxi (at least the rollers) are even more so. In the Maxi, the overall height of the ball can be adjusted by moving the piece that the idler bearing assembly is mounted to in or out on the slots the screws go through. Get the ball as high as you can without binding and the ball won't be a finger pincher. The ball rests in the middle of the assembly and theoretically has 3 tangent points of contact; one in the middle of each shaft. As the ball is rolled the shafts turn the encoder wheels at the appropriate rate. This rotation is detected by the sensors on the small PCBs and fed back as pulses to the game board to be converted to object motion on the screen. The little black box on the PCB contains the emitter/detector pairs. There are two pairs so that movement can be detected in both directions depending on which beam changes state and the current state of the other beam. The holes in the discs let the beam pass through and get cut off in regular intervals which allows the computer to calculate how fast the ball is rolling. If there's no change in the status of either of the beams, the ball is stationary. .__ Key: E - Encoder wheel (screwed on to one end both shafts). | B - Ball-bearing assembly D --E-- D - Detector PCB | | `-- | B | \ B \ | \ B' (for Maxi only) | \ | - \ | Trak- \ | -Ball B | - | | B | B------------------B-----E | | | |__D__| There always seems to be an mixture of dirt, soda and hair inside a Trak-Ball so clean it out while it is open or it will only make the situation worse. Clean the ball and the casing itself with soap and water, and dry. The ball-bearing assemblies also get gummed up and rusty. Use some sort of degreaser, like Brakleen (which is available at auto parts stores, for cleaning/degreasing brake parts) to clean out the bearings. Let them dry completely after cleaning. If the bearings seem to roll pretty good without binding I don't recommend replacing the assembly but do always lubricate them by placing two drops of light-duty oil, such as 3-In-One (R) oil, in each of the six ball-bearing assemblies. The thing that REALLY surprised me about Trak-Ball controllers that have been heavily used (as all arcade game units have) is that the 3 shafts on which the Trak-Ball sits will gradually wear down and become concave. They start out like this: But end up like this: .---------------. .---___ ___---. -- -- -- ___---___ -- `---------------' `--- ---' The wear is so perfectly smooth that, without knowing any better, you might assume that they were manufactured that way. The plastic ball wears down the metal shafts over time which increases the friction and the play of the enclosure and causes the ball to bind and/or hop. All shafts should be perfect cylinders. This way the friction between the shaft and the ball is optimal (minimal). Atari suggested in several manuals that if the wear band exceeds 3/8" along the length of the shaft it should be replaced. If the wear is acceptable, clean the shafts with fine steel wool, removing all corrosion (usually found in the worn area). The biggest improvement always comes from replacing the shafts. After you get the controller back together it still can be a bit rough and need to be broken in. You can get a flat rubber disk that attaches to the end of a drill that's made to attach sand paper to for sanding. What I do is just use the rubber pad WITHOUT ANY SAND PAPER on a drill to spin the ball for a while. Move the pad around to turn the the ball in various directions. This helps smooth out the bearings and also wears down the new roll pins just a touch for sufficient contact with the ball. If you have a Trak-Ball controlled game and plan on keeping it, I recommend buying a new set of shafts (and ball-bearing assemblies if necessary). The play improves dramatically when the Trak-Ball is working well. In fact, buy an extra set as a backup for the future; they are pretty cheap. The best prices I have found on bearings and shafts are at Prestige (formerly known as ANSCOT) who can be reached at 800.456.7277 (or 810.542.5530). Please let me know if better prices are known. I have heard HAPP is slightly cheaper on the shafts and are also cheaper for bearings at $3 individually down to $2.25 in larger quantities. "Midi" Shaft Set: $12.95 "Mini" Shaft Set: $9.95 Bearing Assemblies: $3.99 each WICO has comparable prices for the same stuff but their prices vary constantly so you need to keep checking. I know of no place which carries the Maxi shafts but any of the shafts should be child's play to make for any metal-worker who can use a lathe. Having them custom made should not be too expensive (it could very well be cheaper than retail in any quantity). Every now and then Rick Schieve does exactly that for the Maxi and sells the surplus on the net. You might want to check with him to see if he has any extras if you need a set. Another good place for spare parts is from home Trak-Balls. The Atari 5200 Trak-Ball controller is nearly identical to a the arcade Mini on the inside and is likely to have almost no wear (i.e. good shafts). It has different PCBs (one big one so it can't really be used) and employs the no-idler-shaft design (so there's no idler shaft) but the 2 main shafts, their wheels and 5 bearing assemblies as well as the ball can all be harvested. The ColecoVision "Roller Controller" uses identical parts as those used in Wico brand Trac-Balls with the exception of the PCBs which are different but could probably be very easily modified to work in a Wico controller. Wico controllers use the same PCBs as Atari's did. I believe that many other units also have parts that can be salvaged but I'm not certain (the only one I have checked was the 2600 compatible "Accuball" and it has nothing reusable). The rule should be if you see a brand new (older) Trak-Ball controller for a home system for cheap, buy it and crack it open. I have a limited number of NOS Atari 5200 Trak-Ball controllers for sale for $35 shipped. This will get you a NEVER USED replacement for most of the parts in your mini controller. The best part is you can put your used up parts in it and sell it on the net to a classic HOME game collector for at least $10 (of course letting them know it is in poor condition). The box, manual and mint casing should be worth that much to them! Now what about the case where everything looks good and spins good but the controller still is not working? One thing to check is the orientation of the connector. It is not keyed and can easily be put on upside-down. Doing so does not damage anything even if the game has been turned on so don't worry about that. There is usually a ridge on the wire-side connector which is intended to face the wall on the housing of the PCB-side connector and fit into an reversed ridge to grip the connectors together. Each Trak-Ball has two PCBs so if one of them is working and the other isn't check to make sure the one that isn't working is connected like the one that is. If you can't tell, try it both ways; it won't hurt anything. Next check the PCB itself. Many games have two sets of controllers and this same PCB is also used in many free-spinning (no stop) steering wheels and on spinners (like in Tempest). For Trak-Balls, generally what happens is that one axis works (up and down, for example) and the other (left and right) either doesn't work at all or it reacts as though both directions are one (rolling either left or right always moves to the right). If you swap the PCBs in the Trak-Ball and the problem moves to the other axis then you know the problem is on the PCB. A quick warning about switching PCBs; the Trak-Balls manufactured by HAPP are put together slightly different from everybody else's. If you swap with a HAPP Trak-Ball and yours isn't a HAPP, the directions will be backwards (up moves down and down moves up). The direction pins are the two outer ones on the connector so all you need to do if you want to permanently exchange PCBs with the HAPP is cut and jumper these pins so that they are swapped. It is pretty easy to check the sensors if they are not working. The underside of the PCB has labels to indicate which is the emitter (LED) and which is the detector (photo transistor). First check your emitters since they are the easiest. There's 2 great ways to do this. The best is to get a camcorder and point it at the emitters. You should see a flashing yellow-white glow since Infra-Red falls in the recordable/visible spectrum of the camcorder (note that it is invisible to the naked eye). The next best way is to buy a Radio Shack "Infrared Sensor" (Cat.No. 276-1099) for about $5. It is about the size of a standard large "Band-Aid" (tm) with a sensor strip at one end. You charge the strip by holding it to room light for 10 seconds (fluorescent light works best). Then hold the strip in front of the IR emitter as though the strip were a mirror. You should clearly see a reflection of the IR signal if it is present. If one or both of them is not glowing then you either don't have power getting to it or it is bad. If you can't borrow a camcorder or you'd like to absolutely confirm where the failure is, you can use a meter. You should have have a 1.5VDC drop across the emitter with the power on. The drop will be 5V if open (it shouldn't be shorted since that would cause you to blow fuses and/or your power supply). If the drop is not 1.5VDC then this emitter is bad; if it is 0VDC then your 5VDC power supply to it is bad. Next measure the voltage across the photo transistor and you should see 5VDC going to 0VDC (and back to 5VDC) as you SLOWLY turn the shaft with the power on. If you don't see this (and the emitter you just tested is OK), then this detector is bad. If everything looks OK then, obviously, the problem is somewhere else; perhaps on the game board's switch input buffer. That's a whole different story and you're on your own there. Once you have isolated the bad sensor (usually there is only one), you need to replace it. All 4 sensors are contained in one black box. Unfortunately, the sensors are permanently attached to this box so the best you can do is remove it and cut it in half along the canal. Throw the half with the one bad sensor away (even though the other sensor is good) and replace both sensors on that side (they are the same type). Put the other half back in where it was. Go to Radio Shack or any other halfway decent electronic store and buy virtually any off the shelf infra-red sensor parts you can find. If there is somebody there who seems to know something about their parts (yeah, right) tell them you are repairing a mouse; they use the same exact sensors. When you put the parts on the board, align them so that the face with the "dot" is pointing towards the sensor on the other side of the canal. Be sure to give them the proper height before soldering; you can always adjust the angle of the beam by bending or twisting the sensor but the height is set for good once it is soldered. This repaired side of your PCB will now not have that fancy black cover to keep the sensors aligned and block out stray light but in a properly secured control panel, this won't be a problem. The cheapest place I have found for these sensors is B.G. Micro. They call the parts "matched pairs" of photo sensors. You get both 1 SEP8526 LED (the red case) and 1 SDP8426 phototransistor (the clear case) for only 39 cents. You can order by calling 1.800.276.2206. Here is a very incomplete list of games and the Trak-Balls used in them; updates and corrections are welcomed): Maxi -------------- Football 2 players x2 {Atari '78, BnW} Football 4 players x4 {Atari '78, BnW} Missile Command upright x2 {Atari '80} Super Missile Attack upright x2 {Atari '83ish} Basketball upright x2 {Atari '78, BnW} Midi -------------- Boot Camp x2 {Konami} Crystal Castles upright x1 {Atari '84, 3D} Liberator x1 {Atari '84} Marble Madness {Atari '84} * Millipede upright x1 {Atari '84} * Quantum x1 {Atari '83, Vector} Rampart x3 {Atari '91} * Track and Field x2 {Konami '83} * U.S. Classic Golf x1 {Taito} Mini -------------- Centipede upright x1 {Atari '81} * Centipede cocktail x2 {Atari '81} * Gimme A Break x1 {Sente '85} + Mini Golf x1 {Sente '85} + Missile Command cocktail x2 {Atari '80} * Missile Command cabaret {Atari '80} * Snake Pit x1 {Sente '84} + Unknown size (from KLOV) ------------------------ American Horseshoes {Strata '90} Birdie King II {Monroe '84?} Bowling Alley {Midway '78, BnW} Cabal {Fabtek