Hi,
Along with a dead 4116 (which I recently replaced with a hacked 4164),
my Microcom II+ (Apple II+ clone) has a video problem which has kept me
from using it for the past few years.
Usually when it's cold, the display is a complete mess. As it warms up,
the image becomes clear but in four parts. Each quarter (corner) of the
screen is a mini-image of what should be displayed on the whole screen.
Out of each group of four pixels of what would be displayed normally, each
will be displayed in a different quadrant of the screen.
After about 10 minutes, the screen becomes normal, with occasional "zaps"
and returns to the quartered screen image.
Just about everything in the II+ is TTL, so it's probably just a matter of
knowing which piece of TTL to replace. Does anyone know?
I'm looking at the schematics (for a _real_ Apple II) now, but I have no
idea how to locate the problem because there are several lines leading to
the video output, and the problem chip may be farther back into the
curcuitry and not connected directly to the output.
I know that some of you are fairly expert with Apple hardware.
I want to get the Microcom II+ working because it's the only machine I've
got that's capable of using my Z80 Softcard or my SMC-II Light Pen.
Neither will work in my Apple //e.
Besides, it also has a better keyboard than the //e, once it's been worked
in to cure the 'bounce'.
(As an addition note on the machine's history:
The machine was repaired at the Microcom store in early 1987, and it came
back with a loose, drifty keyboard. I found out the reason was that the
keyboard's curcuit board had been cracked and the keyboard only works if
it's not screwed in too tightly. I'll get around to looking at that after
the video is fixed. It's just one corner that's folded a bit, but there
are traces on there! The keyboard tends to report the wrong characters
when it's screwed in properly.)
--
Doug Spence
ds_spenc_at_alcor.concordia.ca
http://alcor.concordia.ca/~ds_spenc/
Received on Mon Mar 29 1999 - 05:11:35 BST