Apple II+ graphics is all mono, no colors

1 reply [Last post]
Joined: Jul 16 2006
Posts: 81

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.

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.
Joined: Jul 16 2006
Posts: 81

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!