Apple II+ graphics is all mono, no colors

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Last seen: 1 year 8 months ago
Joined: Jul 16 2006 - 17:30
Apple II+ graphics is all mono, no colors

My latest problem with the Apple II+ I am trying to restore is that the graphics is always monochrome, and no colors are displayed.

I do the following to test low-res graphics:

<br />
CALL -151<br />
C056<br />
C054<br />
C050<br />

which turns on low-res graphics, which displays the contents of the text memory, so I get a grid of gray blocks (a few are darker or brighter), but no colored blocks. I have tried it on my Apple IIe, and it behaves the same way except that a few blocks now do have color. I did check video output on an oscilloscope, and it seemed like there is a color signal present (e.g. I saw the 3.58 MHz color burst). Why isn't the II+ displaying any colors? Any ideas what could be wrong?

While speaking of the video; I discovered that there was a tremendous improvement of the video on my small TFT-monitor I bought recently when I reverted the 50 Hz modification on my II+. With the 50 Hz mod, I could barely read some characters, but without the mod, everything is crystal clear.

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Last seen: 1 year 8 months ago
Joined: Jul 16 2006 - 17:30
Fixed

OK apparently the european Apple II plus crystal has a different frequency than the standard 14.31818 MHz. It seems like it is around around 14.24 MHz, only slightly below the standard frequency.

I replaced the euro-version crystal (marked "NYMPH 197-0002") with a C-MAC Hc49 14.31818 MHz crystal, and that makes the video output NTSC, which also made color appear on my monitor!

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