The coin-op game Defender has been a big part of my life, but in recent years I've only played a few times. And due to lack of use, a cross-country move, and a destructive puppy, my Defender machine has fallen into disrepair, with a variety of things that needed repair, replacement, adjustment, or cleaning.

This weekend I decided to get the Defender machine back in business. This post shows a few of the things I did, and also a few details that I find interesting about how these amazing games were constructed back in the glory days of coin-op games.

Defender, like all coin-op games of its era, was housed in a heavy plywood enclosure, with the back locked up to prevent enterprising teenagers from getting at the quarters inside. That lock is a hassle when you're trying to fix things and adjust things at home, so the first thing I did was to remove the lock and replace it with a simple latch from a window sash. Touched up the paint while I was at it.
For ease of access to the game settings controls at the front of the machine, I removed that lock as well, The door just swings open for now, but I'm going to install a magnetic catch like those found in kitchen cabinets.
Nancy the puppy chewed the power cord off while we were storing the machine after moving to Montana. So I replaced the power cord with an extra heavy duty 12 gauge model.
Defender's controls are a pleasure to use when they're in good shape and properly adjusted, but heavy play and corrosion can make them unreliable and frustrating. I used a switch contact cleaning kit to get every control in hair-trigger shape.
I still have the original manual, which is invaluable if you want to play around with the factory settings, or if you need to reset anything. I've noticed they're available online now, so that's good to know if I ever lose it.
The largest chip on the Defender motherboard was the venerable Motorola 6809 processor, which Eugene Jarvis and Larry Demar used in both Defender and Robotron. The 6809 was an 8-bit processor that had some 16-bit features, and was a step up from the Zilog Z80 used in Pacman or the MOS 6502 used in Centipede.
I've had to replace one of those glasses fuses on the right before, but this time around they were all intact.
This board holds the ROM chips, which contain the program code as well as the graphical image data. These chips can sometimes fail, but you can find the data online these days so that you can burn a new chip if needed. I've never had one fail myself, but I've had to reseat chips after they come loose due to moving and vibration.
The Defender power supply has a 110V socket, so that a technician can plug a soldering iron or other tool in without needing to run separate power for it.
After I installed the new power cord and made other changes, it was time to power it up. This is what you want to see: the famous "carpet" pattern on the left (which is essentially a pseudo-random test of memory), followed by INITIAL TEST INDICATE UNIT OK.
The Defender machine back in business, ready to play any time on short notice.

Enjoying the restored Defender machine