Video Game Repair/Williams Defender Problem
Hiya, I hope you have a minute to read this - it's much appreciated. My 1981 Defender upright cabinet has just developed a problem. I'm experiencing involuntary and intermittent actions in the game such as ship moves up, fires, smart bomb, All controls still work, i.e. the ship still responds to joystick movements up and down and all buttons work correctly but somehow the machine is seeing button/joystick pushes that aren't being made by the player. All sound is fine. The machine does enter a set up screen at power up which it didn't used to do. After stepping through the set up options it enters the Williams script welcome screen.
Hope you can help.
It sounds like you have two problems with your game. The first one is likely dead batteries. Have you replaced the three AA batteries on the board lately? If you have, then check the middle toggle switch inside the coin door (on the push-buttons that you step through the test screen with). Try it in the opposite position that it's in now. That should fix the "going into test" problem.
Second, the control issue. Opening the back of the cabinet, you'll see a small 2x4 board with a ribbon cable connecting it to the main board and a long Molex connector with orange wires on it. This is the control input board. Unplug the orange-wired connector and plug it back in. See if this solves the problem. If not, you'll need to pull the board out of the cabinet and inspect the back of it. You'll likely see cold solder joints around the main header pins. They will all need to be reflowed.
Let me know if you need any further help!