Re: Apple iie with switch under case?

[Linards Ticmanis <ticmanis@gmx.de>]

On 12/19/2010 06:35 PM, Sam Latella wrote:
> I just came across an Apple IIe that has a swich underneath the keyboard. 
> Once you flick the switch it goes from the Apple //e to Apple ][.   The
> Apple //e looks like it was built in 1982, and the case itself is a little
> bigger then the other //e I have in use.

Maybe somebody who didn't need the switching between national and
US-ASCII font and keyboard took the international IIe and modified it so
that the firmware ROMs would be switched instead of, or in addition, to,
the keyboard and video ROMs?

> Lastly, everytime I boot up this //e with the switch its hard to read the
> screen... what could be the possible cause, bad board chip?

Maybe the video ROM was replaced by an EPROM and it's starting to reach
the point where bits fail? In that case you'd need to re-burn the EPROM.
You'll need an EPROM burner, but no UV eraser, if you just want to
re-burn the exact same content that's already supposed to be in there.
However if you make a mistake and burn something that differs from
what's already supposed to be in there, it can happen that you'll need
an eraser after that to fix up. I usually use the slow burning algorithm
and burn the chip twice, that should give the burned content maximum
longevity.

If the IIe is a PAL model, the graphics quality issues could be related
to the fact that it has two quartz oscillators, one 14.25 MHz main
quartz, and one 4.43361875 MHZ PAL color carrier quartz. Since the two
quartzes aren't synchronized, their relative speed will drift up and
down a few hertz depending on temperature, causing interference or
what's called a "beat" in acoustics (I'm not sure of the right English
term, the German word is "Schwebung") and thus causing highly annoying
moving moir� patterns to appear on the screen. There's not much you can
do about that except to throw away the PCB and put that of an NTSC Apple
in there, as I did.

-- 
Linards Ticmanis