Re: GR & HGR Do Not Work

[rubywand@swbell.net (Rubywand)]

"Bryan Parkoff" writes ...
> GR & HGR Do Not Work
> 
>     It does not work on Apple II+.  I tried to type GR or HGR, but "@" was
> filled from top upper-lef to the bottom down-right.  I mean that it will
> show only text, but no graphics.  Do you have ideas that it may have
> something wrong with the type of chip in the motherboard.  Where can I find
> Apple II hardware (Not Apple II Reference) book and/or Understanding Apple
> II book?
>     I should be able to repair motherboard myself without sending it to the
> repair deptartment.  It is very hard to find where repair department
> locatio. 
 ....

     Most likely you have one or more chips which are making poor
contact in their sockets. It's a fairly common problem on the II+
because they are so old and have lots of their IC's in sockets.
Various chips have leads which get covered with corrosion and/or work
themselves up in their sockets.

     Besides the 74LS259 at F14 mentioned by Yves, good suspects for
bad contacts are the 74LS02 at B13, the 74LS02 at A12, and the 74LS11
at B12.

     The usual fix is to scootch up and resocket each IC in its
socket. If an IC's leads are dark with corrosion or gunk, mark its
orientation and remove it for cleaning. A light brushing with fine
sandpaper works pretty well.

Note: If you are in a static-prone environment, ground yourself and
any tools fairly frequently-- like, if the II+ is still plugged in you
can touch the power supply case. Or, move to some room that's more
humid and less static-prone to do the work.

     To avoid mixing up IC's or forgetting how an IC is plugged in, it
helps to work with the IC's one at a time.


     If you've never gone through the process for all the IC's on the
board, it may be worthwhile to do it this time. To get to some IC's
this means removing case-- remove the the screws holding the case to
the base, carefully lift off the case, marking the KB connector (with
white-out, etc.) and unplug it.

     It will take a while; but, once you're done, the II+ should be
good for at least 5-10 years before the next cleaning.


Rubywand