Re: Apple II (rev1) instability...HELP!

[mwillegal <mike@willegal.net>]

On Apr 7, 10:33 am, Nama <forums6...@mac.com> wrote:
> On Apr 7, 2:57 pm, Nama <forums6...@mac.com> wrote:
>
>
>
>
>
> > Hi all,
> > Me again.
> > I've recently sold one of my Apple II, and I am moving all my cards
> > over to another rev1 Apple II that I own.
>
> > I'm trying to find out why this system works fine 90% of the time,
> > while the other 10% it crashes and hangs or just displays odd
> > behavior.
>
> > Setup is as follows and is identical to my previous machine:
>
> > 0 - Ram card
> > 1 - CFFA #2 ( (prodos 1.1.1 / contiki))
> > 2 - SSC
> > 3 - empty
> > 4 - Uthernet
> > 5 - Echo 2
> > 6 - Floppy I/O
> > 7 - CFFA #1 (turnkey startup to DOSmaster 1.7)
>
> > Of course I have tried the system with minimal cards and it still
> > exhibits weirdness.
>
> > Symptoms:
> > -Sometimes hangs on boot.
> > -Strange inverted period often seen in top left corner when booting
> > from CFFA #1
> > -Sometimes craches to the monitor
> > -Doing a IN#1 to launch the CFFA #2 always hangs with a strange
> > flashing inverted period in the top left corner. often with corrupted
> > type on the prodos launch screen.
> > -Once it up and running it's usually fairly stable unless I reboot.
> > -Have run a looping game for many hours with no problem, but crashed
> > to monitor as soon as I restart.
>
> > What I have done:
> > Tried a new set of ROMs
> > Run Apple test utils on the RAM and ROM...no problems found.
> > Run the machine from a known good IIe power supply.
>
> > If anyone here can shed some light on my problems, I would be very
> > grateful. I'm hoping the inverted period may be a good clue to whats
> > happening.
>
> > I've uploaded some bad photos here if this helps at all:
>
> >http://web.me.com/lord_philip/apple_1_%26_II/rev1.html
>
> > Much thanks in advance.
>
> > Phil
>
> I love replying to myself...there is some satisfaction in knowing that
> you solved a problem.
>
> THE FIX (as far as I can tell) ...Replace faulty 74LS138 @ H12
>
> From my symptoms I figured there was something up with the slots. With
> nothing in any of the slots the machine seemed to run ok with no
> crashes on power up. So I decided to shotgun replace the IC's that
> were closes to the slots and seemed to have something to do with them.
> Within 15 mins I had found the culprit.
>
> Can anyone enlighten me as to what  74LS138 @ H12 does? In the
> schematic is says I/O selects, but I'm not sure what exactly that is.
>
> Phil

A few days ago, t posted scans of Apple's hobbyboard doc on my blog.

http://www.willegal.net/blog/?p=1447

 There is a separate I/O select for each slot, except 0.   It is often
used
to select the last 256 bytes of each peripheral card's ROM.

Regards,
Mike Willegal