Re: Apple IIe TV output quality

[Cyril Thibout <info@pulsar-informatique.com>]

Le samedi 29 décembre 2012 20:30:56 UTC+1, Cyril Thibout a écrit :
> Hi
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> I just purchased an Apple IIe (rev B, PAL, 80col card) on ebay and tried to connect it on a flat TV composite input.
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> Wile in Hires the image is perfect, in text mode the background is greenish with parasites. in 80 col mode I can barely read the characters.
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> Is that normal? Should I use an old TV (non flat) ? 
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> I must add that on the green monochrom monitor the text mode is perfect in 40 col mode. in 80 col mode on the monitor the characters are somewhow truncated.
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> Should I check some components?
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> any idea please?
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> thanks
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> 
> cyril

Hi again

After may attempts here is what I've done :

- discovered the problem is that the bit 5 and 6 of main video ram is overwritten by bit 0 of aux video ram (bit 7 is never used in double hires). 
- however this problem is only a video signal problem: the main memory is not really overwritten. everything occurs AS IF two bits of main ram where modified by bit 0 of aux ram. so the problem is a video signal generation issue in 80 col mode
- KERNEL OK
- switch the 80 col /64 K board --> but the problem remains
- switch the video ROM --> but the problem remains
- swith the LS166 --> but the problem remains
- swtich the LS374 --> but the problem remains
- switch the IOU  --> but the problem remains

I posted some screenshots at http://www.vintage-computer.com/vcforum/showthread.php?35069-Looking-for-some-help-to-solve-an-Apple-IIe-video-weird-problem! 

any idea please?

thanks

cyril