Re: Extended 80 column card issue

["Michael J. Mahon" <mjmahon@aol.com>]

Linards Ticmanis wrote:

> A bad logic chip would be more likely to cause complete failure of the
> card, IMHO. All data bits from and to the card go through these buffers,
> one of them for video data (such as characters being displayed on an 80
> column screen), the other for CPU data (such as characters being written
> to an 80 column screen); so you wouldn't see a working 80 column screen
> if one of them had failures.

But any high address line could be bad and the text and hi-res
screens would never know about it...

and:

> One other thing to try:
>
> Boot ProDOS into BASIC, then store some files to /RAM filling it up as
> far as you can (load BASIC programs from disks and save them to /RAM for
> example). If you can re-load them without errors, chances are the card
> is working as it should.

Unfortunately, only a real memory test will provide any assurance
that the memory is functional.  All "use" tests like those above
are insensitive to a large fraction of problems.  (Though Murphy's
law pretty much guarantees that if you're actually trying to run an
important app, a flaky memory chip will stop it in its tracks.  ;-)

-michael

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