Battlezone Cabaret – Retrace line issue SOLVED!

Battlezone test mode showing retrace lines.

No sooner had I gotten my 1980 Atari Battlezone Cabaret home and working, when a small but potentially annoying video issue became apparent.

If you are unfamiliar with the differences between Raster and Vector monitors, here is a brief introduction:

On my game, there was something going on with the Z-axis video circuit, which was causing a line to remain visible between vectors. These are known as Retrace Lines. This was something that was completely tolerable at first, since I was going from NO Battlezone to an imperfect Battlezone, but I was also quite aware that this would be a serious annoyance before too long.  Most of the time this can be addressed by adjusting the brightness and contrast pots on the monitor’s deflection board.  In my case, adjusting wasn’t doing the trick, so something else was at work.

I was lucky enough to be able to run some tests on the PCB which excluded the monitor as the source of the problem, so I knew I was looking at a board issue. This is a great example of a time when the game’s schematics would be really handy.  Luckily, these are available widely on the web. If you can’t find them, look right here:

Close up of schematic sheet 2B, including IC P9.

With a little guidance from some KLOV members, I was able to use my logic probe to work my way back through the Z-circuit, and after making a few missteps, and replacing some parts that turned out not to be the source of the issue, I eventually discovered that the connections from the IC at location P9 on the PCB to the IC at N9 were being held high when they should be pulsing. The inputs to P9 were were normal, which suggested that P9 (which is a 74LS164) was likely the source of the problem. I removed the IC, soldered in a socket and inserted a new 74LS164.  Happily, this seems to have solved the issue completely.

With that issue fixed, the PCB was now running pretty much perfectly.  The next step was to address the joysticks, which, while functional, also showed some signs they they were in need of some help.