Apple ][+ no graphics mode

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Apple ][+ no graphics mode

Hello All,

 

I'm trying to revive a Rev D RFI Apple ][+ board and running into an issue.

I can't get it to flip into either lores or hires graphics mode.

 

HGR command just returns to a viewable prompt and GR will display text garbage (where graphics is expected) with the normal viewable prompt and text lines at the bottom.

I can switch back to TEXT mode fine.

 

Going through W. Gayler's "The Apple II Circuit Description" (Chapter 8) the 74LS151 at A9 seems to handle the soft switches.

I've replaced it from a known working board and same issue.

 

I proceeded to swap out A3, A8, A10, B4, B9, F14 and still the same issue.

Thought I might have a short but bottom traces are clean.

 

I'm stumped at the moment.  

I'm digging more into how the soft switches are set and breaking out a scope to check but any advice is appreciated.