This appears to me to be an intermittent trace on the main board's video
addressing logic I'd look in the counter chains. Careful examination of the
boad may enable you to find it.
Dick
-----Original Message-----
From: Doug Spence <ds_spenc_at_alcor.concordia.ca>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
Date: Monday, March 29, 1999 4:18 AM
Subject: Messed up Apple (clone) video
>
>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 - 11:49:16 BST