Apple II no video modes

I have a Apple 2+ that had a ram error but this has been solved by changing all the ram - the ram passes a soak test ok.

But

when any video mode is accessed the machine just displays nonsense - no graphics at all.

is this a bad rom or video error of some kind. any help please....

mike

Interesting... The Low and High Resolution Video is not working, but the Text is fine...

ROM would be the Characters themselves, or the BASIC Language, but not toggling the Hardware Switches themselves.

Has speedyG said anything about this?? He is pretty knowledgeable about such things..

hello mike,
i was today working the entire day at the completion of the apple 1 ram-expansioncard.... so at the moment the autorouting tool is working and i just made a short skip over here....
the very first point i am missing is:
how much ram is inserted ? if it´s only 16 kB for basic examination - then graphichs won´t work !
For display of graphic pages it´s required that the apple is populated with the entire 48kB on board....
which revision is that board ?

the most important chips at the apple II for switching to graphics are:
the 74LS04 at location C11
and 74LS257 at location C12
as well as the 74LS257 at location J1
and 74LS08 and location H1 and
finally last not least the 74LS139 at position F2.

All of the here listed chips are related to the so called graphic-switching of the graphic pages.....
so first of all i would control all of this chips for correct seating ( no bent legs underneath of the chip
but not in the socket.... ) and then i´d try exchanging this chips one by one with a working system
to detect the faulty one ( my preference is one of the 74LS257´s or the 74LS139 )
but of course this will be only valid task, if the RAM is completely populated with at least all RAM on Board
i.e. 48 kB RAM..... the language card is not required for testing....
sincerely speedyG

hello mike,

<< SNIP >>

the most important chips at the apple II for switching to graphics are:
the 74LS04 at location C11
and 74LS257 at location C12
as well as the 74LS257 at location J1
and 74LS08 and location H1 and
finally last not least the 74LS139 at position F2.

All of the here listed chips are related to the so called graphic-switching of the graphic pages.....
so first of all i would control all of this chips for correct seating ( no bent legs underneath of the chip
but not in the socket.... ) and then i´d try exchanging this chips one by one with a working system
to detect the faulty one ( my preference is one of the 74LS257´s or the 74LS139 )
but of course this will be only valid task, if the RAM is completely populated with at least all RAM on Board
i.e. 48 kB RAM..... the language card is not required for testing....
sincerely speedyG

I hadn't thought about the RAM, but the Second Picture is for the Lo-Res Graphics, which uses the Text Display RAM.. The Third Picture appears to be Hi-Res, and the Fourth Picture show that a Lower Case ROM has been added to this Apple ][+.

I am going to suspect the 74LSxxx Logic.....

Hello Mike,
in fact thats not realy true....
there are 2 books with excellent explenation of the entire Apple II including also detailed explenation of the videosection and the related circuitplans.....:
The Apple II circuit description from Winston Gaylor
and
Understanding the Apple II from Jim Sather
both are availiable for download at the Apple Documentation Project at:
http://mirrors.apple2.org.za/Apple%20II%20Documentation%20Project/
select there the directory:
Books/
and within that directory select:
W. Gayler - The Apple II Circuit Description.pdf ....... 33M
and
Jim Sather - Understanding the Apple II.pdf ............ 80M
This are the 2 most valuable books, if you intend to repair Apple II models.....
and besides there are also excelent books for repair and maintainance of the Apple IIe and the IIGS !
It surely is highly recommended to spend some time in that site and download several books in excelent scan quality !
sincerely speedyG