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Troubleshooting Light Gun Issues

Troubleshooting Light Gun Issues

While joysticks and buttons are the most common form of player controls on arcade games, many different types of controls have gained popularity over the years. One of the more recent innovations in video game controls is the light gun. Light guns were very popular in the early mechanical coin-operated machines of the 1920s and 1930s but it wasn’t till the mid-1980s that the technology would be available to allow light guns to interact with video screens. Ever since that time, we’ve seen an explosion of light gun games on the market. With so many light gun games on location today, knowing how to repair the issues related to them can be a valuable skill. In this post, we will discuss how to troubleshoot some common issues with arcade games that use light guns.

Troubleshooting Light Gun Issues

Before we begin, we would like to mention that the main focus of this post is on light guns that use a light sensor. There are some light guns that use potentiometers to determine the position of the gun target on the screen. These light guns are typically physically attached to the arcade cabinet (usually at the bottom of the gun grip) with the potentiometer values changing based on the movement of the gun. These type of light guns are less common so we are going to focus our efforts in this post on the light sensor based light guns.

The majority of questions we receive about light gun based arcade games are related to aiming and targeting. In other words, the light gun is having trouble locating the desired target on the screen. Sometimes a light gun’s aiming might be off by just a hair in one direction while other times it might not even be locating anything on the screen at all. Our first troubleshooting tip for this type of issue is to try and calibrate the gun. Most arcade games have a test mode that you can enter by pressing a button located either in the coin door or somewhere else inside the cabinet. Once this button is pressed, you should receive a menu on the screen with several options. Most light gun games will have either a gun check or a gun calibration option in this menu. Please consult the manual for the game if you have trouble locating this option. Select this option and follow the on-screen instructions to check/calibrate your light guns. Of course, the test menu also gives you access to several other game options besides the gun check/calibration option. We hope to release a post discussing the test menu and these other options in the near future so stay tuned for that.

There’s a chance that you might still have issues with your light guns after going through the gun check/calibration in the test menu. Sometimes a light gun will have problems registering certain parts of the screen such as the corners. If this is the case, you might start trying the brightness adjustments on your monitor. At this point, we recommend consulting our post on Adjusting An Arcade Monitor so you can get familiar with the different potentiometers and what they control. So, you may be asking yourself what the monitor picture has to do with the light gun working properly. Keep in mind that the sensor in the light gun interacts with the light from the monitor and the picture on your monitor tends to get weaker over time due to the wear on the electronic parts. With that said, most monitor typically have 2 brightness adjustments: one on the chassis and one on the flyback. We recommend turning the brightness up on both until you see the raster lines (diagonal, white lines) on the screen then turn them back down just below where these lines disappear. This is typically brighter than most people like their picture but it can make a big difference in how the light gun registers the location on the screen. Keep in mind that if you’re having problems adjusting the brightness to this level that you might need to do some work on your monitor (see Installing A Cap Kit).

Sometimes the physical location of the cabinet can cause you to have issues with your light guns as well. For example, placing an arcade cabinet under bright lights (such as a fluorescent fixture) can cause reflections on the screen that confuse the light sensor in the gun and cause targeting issues. The same goes for natural sunlight if the cabinet is too close to a window. Make sure that your cabinet is positioned in such a way so that the reflection from bright lights does not cause the light sensor in the guns to malfunction. Also, discolored areas on the screen can affect the location that the light gun sensor is trying to target. You might need to rotate the cabinet 90 degrees or degauss the monitor (see Using A Degaussing Coil) to help alleviate these type of discoloration issues.

Now, there’s a chance that you could still have issues after checking/calibrating the gun in the test menu and adjusting the monitor. In this case, you are probably having some sort of issue with the light gun itself. The first thing to check on the light gun is the lens which is located inside the barrel. Try cleaning this lens with a cotton swab and some glass cleaner to see if you can remove any dirt and/or dust from it. You might need to replace the lens if it’s scratched or damaged. At this point, you will need to open up the light gun. Most light guns use security screws (such as Torx) in order to keep kids and other individuals from opening them up. You can purchase a security set that contains the bits you will need to open up the light guns if you do not already have a set of your own. Keep in mind that you will need a 1/4″ nut driver or bit holder in order to use these bits.

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Once the light gun is opened up, we can replace the lens and check out some other parts that might be causing issues. Some light guns have protectors in front of and holding the light sensor. We recommend cleaning these protectors using the cotton swab and glass cleaner mentioned earlier. After you clean these protectors, make sure that the light sensor itself is positioned correctly (i.e. pointing straight at the lens, not off to one side or the other) and that the legs of the light sensor are making a good connection to the circuit board (i.e. the legs aren’t bent, the solder joints are not cracked or cold, etc.). You might also do a visual inspection of the circuit board just to see if there are any parts or burned spots that could be causing issues. If you suspect there maybe a problem with your board, the best thing to do is just replace it. You can try to repair this circuit board yourself but the surface mounted parts on it can be a real hassle to replace if you don’t have the right tools. You can get replacement light gun circuit boards for around $25 from Suzo/Happ and other retailers.

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Two more things to focus on inside the light gun would be power and wiring. Most light guns require +5 VDC to function properly. Measure the voltage on the light gun to make sure it is correct. Keep in mind that light guns usually don’t hook up to the wiring harness and instead use separate connectors to connect to the main board. Sometimes the pins on the connectors of the main board or the light gun circuit board can become bent or have other issues (such as cracked or cold solder joints). Check for these problems and repair them accordingly. Also, make sure that the wiring between the connectors is in tact and that it’s making a good connection on both ends. At this point, you might reassemble the light gun and see if it is working properly.

Just a quick note: some light guns have a solenoid or coil inside of them to create a sense of recoil (or kick) when you pull the trigger. This is not necessary in order for the light gun to work properly. You can purchase this solenoid from Suzo/Happ or other retailers if you would like to repair (or add) this feature on your light gun.

Unfortunately there is not a cut-and-dry solution for getting any one light gun game to work properly. Each light gun game (and cabinet) has it’s own set of challenges and obstacles to overcome. Hopefully the tips mentioned in this post will at least give you some ideas on how to solve the problems you are having with your particular light gun game. Please leave any questions or suggestions in the comments section below.

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Comments
  1. TJ Beyer

    If you’re tired of broken opto legs from the gun being dropped on the floor repeatedly, try soldering a piece of wire (2″-3″ is fine) to the opto leg, and the other end to the PC board where the opto would have normally been soldered on. Repeat for the other leg, paying attention to the original polarity of the opto in relation to the board. Now when the gun is dropped and the PC board shifts around inside the gun shell, the opto can also shift and not break off.

    Games like CarnEvil, Johnny Nero, and Sports Shooting/Ranger Mission where the gun has half a mile of wiring and a dozen connections/aux boards, the +5v can get pretty low by the time it reaches the gun board. Cutting out some of the excess connections for the +5v can help significantly with gun tracking on these games (if your +5v inside the gun is low). I won’t go into details here — If you’re comfortable working on games, you can probably figure out how to run an extra wire from the power supply to the gun :)

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