Strange behavior of the color killer on Apple II plus

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Strange behavior of the color killer on Apple II plus

The color Killer is working strangely on my machine....

when the machine looks "idle" it's working I have a black and white screen

but as soon as I use the floppy disk  (for example command:  "catalog")

the caracters are colored with strange patterns mostly blueish / redish...

when the floppy stops I get back the black and white

 

I slighlty reduced the value of the resistor, the problem partly disappereared

but still exist while using the floppy disk

 

(before it was present each time I was using an extension board like the language board

or a legend memory board

 

any idea on how to fix that

 

thanks to all

 

 

 

 

 

 

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The color killer circuit

The color killer circuit really only wounds the color burst signal, so it may actually be on the verge of showing colors on the particular monitor you are using.  The additional load of the floppy drive on the power supply may change system behavior enough to let the color burst leak through a bit more so that your monitor starts showing color.  I suspect that there is nothing wrong with your Apple II.  You will likely have a different result if you try a different monit0r, which is either more or less sensitive to the color burst portion of the NTSC signal.

 

In short, the color killer circuit is not a very good design feature and mileage will very depending upon your particular monitor and the rest of your setup.  It would have been better to use a digital gate to turn the color burst completely on or off, rather than the transistor that they ended up using, which just attenuates the color burst.

 

regards,

Mike Willegal

 

 

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Inold power supplies it might

In old power supplies it might indicate that that  +12 Volt rail is not stabil
and suffers when floppy turns on so that + 5 Volt rail gets bad leackage...

this would cuuse the color killer transistor to  show strange effects....

check R5 1k and C2 47pF for possible damage or drift of value due to age
see Apple II Circuit description at page  216

 

sincerely
SpeedyG

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Strange behavior of the color killer on Apple II plus

Thanks to all,

 

I'll try to find a way to fix it,

I'll give you the result

 

 

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Joined: Jul 5 2018 - 09:44
Posts: 170
I would concur with speedyG,

I would concur with speedyG, power supply voltages being off can cause all sorts of weird side effects, including the kind of behavior he describes when the high draw of a floppy drive pulls voltages down.

 

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