Re: Apple II+ Display Question

[Rubywand <rubywand@swbell.net>]

Robin writes ...
> 
> I've recently acquired an Apple II+ and have a question about the
> display hardware.
> 
> I was under the impression that all Apple II+ computers had the
> "color killer" modification that was made since the second revision
> of the Apple II.  However, I am seeing the green and violet fringe
> around white text characters.
> 
> Am I wrong in assuming that the "color killer" has been implemented
> on all Apple II+ computers or is there a possibility that something
> may be wrong with my computer?
 ....

     According to the Apple Reference Manual, if you have a II+ you have the
Revision 1 board mentioned by Jonathan. It should kill color for plain Text
displays-- i.e. full-screen Text displays.

     You can not normally kill color for the Text window displayed beneath any
lores or hires display (unless you kill color for the entire display).  Getting
just the Text window in B&W requires a mod to your monitor plus a line going to
a point on the A2 motherboard.

     If your II+ displays all-Text screens with colors, two possible
explanations are ...

o- You have an early Apple II which was modified to work something like a II+
by swapping in II+ ROMs or PROMs. (This would be a good bet if the logo on the
case says "Apple II" instead of "Apple II Plus".)

o- Something is blown or not making good contact on your II+ motherboard.


     If it looks like your Apple II is a for-real II+, there are a couple
directly related components to check.

     One possibility is a bad 2N3904 color kill transistor (Q6). If Q6 is blown
and does not switch ON properly, it will not shunt the color burst signal to
Ground and all displays will show colors. (If the 2N3904 is suspect, you can
relace it with any general purpose NPN transistor.) 

     Another thing to check is the 74LS259 (IC F14).  If it is making poor
contact on certain pins (mainly, Pin 4) the color kill will not work. Try
scoothing it up and resocketing it.

     If resocketing does not fix the problem, mark which end has the notch and
how it sits in the socket, remove it, clean the pins, and put it back for
another try. If none of this works, the IC may need to be replaced.



Rubywand