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

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

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.
>
> Sounds like good reason to suspect the DRAM.
>
> Completely apart from the disk, can you run Applesoft?  Does the
> machine function minimally without a disk?  (If it does, then you
> can get into the monitor and key in a short memory test program.)
>
> A simple memory test would, for example, write the low byte of
> each location's address into memory, then read it back and compare,
> then do it again writing the complement of the low byte, etc.

Yep, I can get into Applesoft - I was thinking about using a variant
of the memory test that Mike had up at his page.

> The "easy" way to go is to replace all the DRAM, but I'm guessing
> that you don't have that many 4116 chips.

I have another motherboard coming in the mail, so I'll soon have
4116's to spare!

> It is unlikely that all 8 DRAMs in a "row" are bad, but you could
> have 2 or 3 scattered in more than one bank that could cause this
> problem.

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.

I think tonight I'll pull out the rest of the RAM and see what happens.