Alien 3: The Gun
The player one gun on the machine didn't have any recoil / feedback when I got it. The operators manual points to fuses and DC motor bushes as being the culprit for this failure so these were checked first. The design of these cabinets makes these checks very easy. Fuses are located in the service panel and the bushes are easily accessed by removing an access panel on the gun assembly. In my case both the bushes and fuses check out fine BUT the player one gun motor was really loose compared to the second player gun. Time to investigate...
To diagnose the issue(s), the gun shells needed to be removed. This process was straight forward with the correct security driver bit but there were a few screws that were too corroded - this is where the extractor screw sets come in handy. I cannot count the number of times that the extractor screws have helped me during restorations. To use them, you drill an appropriately sized pilot hole. Once that's done, you insert the extractor screw into the hole and turn anti-clockwise until it bites. Of course the screw is no longer usable but they are easily replaced.
Once the plastic covers are removed, you can see how over-engineered these guns are. (Sorry about the upside down image - I couldn't get it to show correctly). The gun is in two main sections an upper section and a lower section. The upper section slides along the lower section on one axis, creating a backward and forward motion and simulating the machine gun recoil.
Unlike other gun games that use a solenoid to simulate the recoil, these Sega guns run a bushed, DC motor connected to a cam-gear. The rotation of the cam-gear pushes the upper section forward along the slide and then a spring helps to recoil the gun back to its start position. It's a very clever design from a haptics standpoint. The addition of the spring in the front of the gun changes the behaviour of the slide during forward and reverse motion.
Once the gun was dissembled, it was clear that the cause of the loose motor was due to loose fasteners holding the motor to the main assembly. To remove the motor from the upper section, there are four bolts that need to be undone plus the coupling that connects the motor output shaft to the input shaft of the cam gear.
Once the motor was free of the upper assembly, the reason for the loose motor looked clear - at least at first. The four bolts that held the motor to the bracket were very loose, but when I tried to torque them up, they had no bite.
The reason the screws wouldn't torque up was because there was no thread left on them!
I replaced the M4 screws with hardened M4 bolts, and new spring washers. I figure that the hardened bolts will eventually wear out the thread in the hole but I am not too worried about that given that these machine is only going have home use. Even if the thread holes fail, I could easily drill the holes out and re-thread them to M5 or M6 at a pinch.
This bit of work resolved the issue of the loose motor assembly. In my next post, I will share how I got on with the electronic repairs required for the recoil on gun one.