Apple //e Video Tweak Avoids Color Killer Mod

During the break I spent some time playing with my Apple //e, recently set up after some 25+ years of neglect. Last year I replaced the PSU mains cap (common failure) and explored the excellent Apple ][ Disk Server and the Game Server – who could have imagined the cassette port transferring at 9600 bits per second! I didn’t have a joystick, which ebay has since solved, but given my vision I won’t be making any high score tables.

The //e is connected via composite video to my Samsung 27″ monitor/TV. I was very disappointed with the clarity of text, 80 column mode was unreadable even with the monitor on maximum sharpness. I remembered a far better display on the tube tele in the 80s.

The computer has a “text mode” switch on the motherboard. This cleared it up, but I don’t want a monochrome //e. I also noticed the monitor did give a clear picture for one second when I connected the video signal.

I figured I was suffering from chroma signal bleed through, forcing my monitor to interpret the signal as colour, and I’d need the color killer mod. This seemed confirmed by the picture clearing up if I snubbed out the PAL colour chroma oscillator with my finger.

My //e is a PAL version and I played with the 2 PAL chroma pots which adjust the background tint as a side effect of balancing the colour signal. I noticed they had no effect in text mode. Yet the text was equally blurry in text or mixed text/graphics mode.

Before the mod, I decided to at least set the chroma trimpots properly (for a black background in graphics mode) and I also tweaked the chroma frequency capacitor trimmer (this affected the moire patterns but not much else). I did this in mixed text/graphics mode with some text at the bottom.

To my surprise, as I approached the optimal position for the two chroma trimmers, the text sharpened up better than it had ever appeared on this monitor.

More importantly, in full text mode, it still looked great, as well as in 80 column mode and even 80 column + graphics. The chroma pots were still having an effect in text mode, even though the background colour didn’t reflect their setting.

I suspect that balancing the chroma signal properly prevents some noise reduction system in the monitor from kicking in, leaving a full bandwidth display in both text and graphics modes. In graphics mode the individual colour pixels are distinct, the best I’ve ever seen a PAL Apple ][ do (having never experienced a pure NTSC set up, let alone RGB).

So now no color killer mod needed.