Re: 80 column mode on //c

[supertimer@aol.com (Supertimer)]

daimyo@powersurfr.com wrote:

>I have an apple //c that displays garbage characters when in 80col
>mode.  (40 col mode works fine).  Strangely, every second character is
>garbage, as if offset by some value out of normal ascii values in the
>text image of RAM.  The machine also complains it does not have 128k
>on some applications.  Is the RAM bad?  Does this problem sound
>familiar to anyone?  Can it be fixed? etc etc

Probably the RAM is bad.  The IIc divides its 128k into 2 banks
of 64k.  The screen memory is also divided into 2 40 column
screens that are then interlaced to make 80 column.

If the particular memory chip in one of the 64k banks is
faulty, every other column in 80 column mode will be messed
up.  Since the problem only shows up in 80 column mode,
not 40 column mode, the chip is hiding in the second 64k
bank.

You'll need to desolder the faulty chip and solder in a
replacement.