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Re: Apple ][+ With Bad HGR and GR Modes

Matthew Russotto wrote:

In article <1128833071.129836.327030@g14g2000cwa.googlegroups.com>,
JNorrid <jnorrid@att.net> wrote:


Question: Since the coffee spill may have seriously corroded the
non-visible area of the sockets, should I replace all of them or is
their some kind of solvent that I could dip the board into? Socket
replacement will be brutal, but I'd do it if that is what it took to
get this thing goin' again. Your help is greatly appreciated.



Distilled water is the safest solvent.  You might follow up with
alcohol to speed drying.  However, your symptoms pretty much narrow
things down to the text/graphics soft switch not working.  So you
might want to start with the 74LS259 at F14.  Pin 4 is the
text/graphics switch.  From there it goes through a resistor (R27,
4.7K) into a 2N3904 at Q4 (I assume a discrete transistor; I'm looking
at a schematic but I don't have a board nearby), and also into a
74LS02 at B13.  The problem could also be on one of the two 74LS174s
at B5 and B8.  I think any further up would cause other problems.


Could that be the same 74LS02 at B14 that he reported as having
a cracked package?

Though ICs occasionally overheat because of an internal failure,
they can also overheat because of an external short on an output,
for example.  There is probably another failure that caused the
'02 to overheat.

-michael

Music synthesis for 8-bit Apple II's!
Home page:  http://members.aol.com/MJMahon/

"The wastebasket is our most important design
tool--and it is seriously underused."