Apple II Plus - defective color killer?

2 replies [Last post]
Joined: Jul 21 2008
Posts: 18

I have a II+ (rev 07) and I've found that when I adjust the pot to a more intense signal, the color killer in text mode abruptly fails and I get green/purple bleeding. If I adjust it even higher, the green/purple switches to red/blue.

The color killer only works for very low intensities - hardly bright enough to be usable.

I've tried replacing 74LS259, with no effect. Any ideas on what else I should check?

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Joined: Jun 5 2008
Posts: 385
Your machine is not broken -

Your machine is not broken - the implementation doesn't completely eliminate the color burst, just greatly reduces the level of it. Some monitors can still lock on to this reduced color burst signal. I'm thinking that a better implementation would have been to kill the color burst at the output of the clock circuit, not at the final video output. This would have left no reduced signal for monitors to lock onto.

Mike Willegal

amauget's picture
Joined: Jan 3 2011
Posts: 249
You can also try


Well, it's been a while since the last post.
Another thing to do (thanks to "Understanding the Apple II") is to increase the R6 value from 2.7K to 4.7K or higher.

Hope it's not too late !


Apple II forever