Tempest Restore

I bought the Tempest cab from a friend of a friend Justin R. It was my second machine. The first, an Asteroids Deluxe, I had also bought from Justin a few months earlier. I felt as though it was important to start looking for another project soon after having finished the Asteroids restore. I wanted an opportunity to test what I had learned the first time through, to attempt to do it with as little help as possible.

My ideal cabinet is one that is fun, broken in some way, and in reasonably good cosmetic condition: the side art is intact, the control panel overlay isn’t worn through or covered in cigarette burns, the marque is clean. Machines in this condition have two important characteristics; they are affordable and they’re fun to fix!

Turns out that Justin had an old Tempest in the back of his garage that he’d planned on fixing but hadn’t gotten around to. When he bought it the game started up but the monitor wasn’t working (playing blind), he sent me the following pictures:

Last but not least, Tempest is one of the greatest of all time arcade games, and Justin is willing to sell it to me for a reasonable price. So what’s a man to do but drive down to a tiny little rural town outside of Tacoma. To a suburban home with a two car garage filled end to end with Arcade and pinball machines. To take home a beautiful broken old game from 1981.

Tempest was released by Atari in 1981 (the same year as Asteroids Deluxe!), it was the first of a handful of color vector games released from ’81 to ’85. It’s an awesome, frantic, colorful, and completely unique game.

Atari machines of this era were all composed of roughly similar components.

One fun thing is that these machines were built with the assumption that operators would be required to maintain and repair them. Subsequently they came with an astonishing amount of high quality documentation. One of the first and most important steps to take when beginning a repair is the familiarize yourself with the machine and documentation.

Once the machine is home I begin a process of general diagnostics. Many individual parts: capacitors, transistors, resistors, integrated circuits; that make up these games can fail with time and use. I clean and check all the components in the cabinet then begin testing each one starting from power and moving towards the monitor.

When I got everything out on my bench and started testing I only found a minor issue on the AR board (the 12v DC line was dead indicating a dead 7812 voltage regulator). Testing the +12VDC I was only reading 1.2VDC tracing back from the text lug the next component back is the 7812 Voltage regulator, but the voltage leading in was correct (22VDC). This indicates a failure of that part, I’ve removed it and ordered a new replacement for the next round of testing.

So I connected all the components together and flipped the switch. Unfortunately out on the bench the game wasn’t playing blind. After some double checking of my intuition and that I was getting appropriate voltages on the board I was convinced that the game wasn’t running.

Debugging a board like this is debugging a computer, to debug it we have to understand how it’s supposed to work. Once again we are lucky and many of the functionings of this computer were meticulously documented by Atari.

The clock circuit works by taking outputs from an oscillating crystal and feeding them to a “counter” IC. This circuit in turn has the effect of splitting that signal into a number of separate frequencies (it turns out that the “counting” functionality of this IC isn’t used at all). The new frequencies are then passed onto a handful of other circuits including the CPU.

In the above picture we can see the clock circuit, notice the oscillator as well as the C4 and B4 counters. As a brief note it’s worth describing how Atari labeled parts on their boards. All the ICs are in a grid with rows labeled A to Z and columns 1 to N. So when describing a chip as C4 we are looking in the C row at column 4. As an example the chip to the left of C4 picture would be labeled C5. As a further note all the ICs are in what are called DIP packages (dual in-line package) whose pins are labeled from pin 1 counterclockwise to pin N.

In the case of the Tempest I was working on I could trace a correct signal from the crystal to pin 5 on the Counter C4, but there were none of the output signals that should have been seen on pins 14,3,2,6, and 7. It isn’t uncommon for the ICs on these boards to fail over time and that appears to be the case with this one. Surprisingly this was also an error that I found on my Atari Deluxe, perhaps these 193 chips are starting to fail.

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