Re: Apple ][+ gravely ill - seeking assistance :(

["N.N. Thayer" <nnthayer@hotmail.com>]

On Jun 10, 6:22 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> N.N. Thayer wrote:
> > On Jun 10, 3:05 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
>
> >>N.N. Thayer wrote:
>
> >>>On Jun 9, 7:52 pm, "N.N. Thayer" <nntha...@hotmail.com> wrote:
>
> >>>>On Jun 1, 9:19 am, "N.N. Thayer" <nntha...@hotmail.com> wrote:
>
> >>>>>On Jun 1, 8:53 am, schmidtd <schmi...@my-deja.com> wrote:
>
> >>>>>>On Jun 1, 9:22 am, "N.N. Thayer" <nntha...@hotmail.com> wrote:> Hmmm.  Well, now I can get to a prompt and work there indefinitely,
>
> >>>>>>>but if I try to load anything off a disk, including ones that I know
> >>>>>>>are self-bootable, I get garbage characters and the drive simply
> >>>>>>>spins.
>
> >>>>>>>I've swapped disk controller cards, and tested the drives on another
> >>>>>>>machine, so I know it's not either of those.
>
> >>>>>>Have you swapped power supplies?  Failures might be occurring because
> >>>>>>voltages drop too low to sustain life while the drive draws its power
> >>>>>>to spin up...
>
> >>>>>I've got another power supply coming in the mail, a //e model.
>
> >>>>Hmm!  Further testing:
>
> >>>>1. Swapping power supplies has no effect.
>
> >>>>2. If I boot a known good disk with a full onboard bank of RAM, I get
> >>>>garbage and a constantly spinning drive.
>
> >>>>3. If I do the same after having removed RAM E3 through E10, I get a
> >>>>beep and it drops me into the monitor.  The drive spins down.
>
> >>>>4. If I replace E3 through E10 with RAM retrieved from a known working
> >>>>Language Card, and boot the disk, I get the same result as in #3.
>
> >>>Sorry - for #4 I meant to say the same result as in #2.
>
> <snip>
>
> > Well, what I find odd is that when I replace E3-E10 with a completely
> > different set of chips, I get exactly the same result as with the old
> > set - but if I remove them completely, leaving only C and D, I get
> > dropped into the monitor when booting a known good disk.  It seems
> > unlikely to me that a chip in both sets would be failing in a totally
> > identical way... also, when I ran RAM tests from the ][+ Diagnostics
> > disk (back before the computer decided to not boot disks at all), it
> > all checked out fine.  Made me wonder about other chips, maybe the
> > 74LS174's or something.
>
> Actually, if the DOS on the disk is a "slave" DOS, then it will
> not adapt to the actual amount of RAM in the machine it's booted on.
>
> An Apple ][ must have "bank 0" present to operate, but I don't know
> which bank is in row E.  You either made your Apple into a 16KB or
> a 32KB system by removing that row, and it would take a "master"
> DOS to boot on it (unless, by coincidence, your "slave" DOS matches
> the reduced size of the system).
>
> -michael
>
> AppleCrate: An Apple II "blade server"!
> Home page:  http://members.aol.com/MJMahon/
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."

Well, after replacing every single IC on the (Rev 7) motherboard with
ones from a known good (Rev C) motherboard (except for a few chips
that didn't match up), and still seeing failure... I ended up just
replacing the motherboard.  Not happy about it, though - total
replacement was a last resort. :(