Re: PET 3032 issue

Ok some progress.
It turns out that the petester.bin image only tests one 16K bank, not
both (on my board, only the innermost bank).
Swapping the CAS lines (R41, R42) did show some errors and I
substituted one 4116, I thought I was lucky since the petester didn't
show any error anymore, so I put back the original kernel ROM and it
did indeed boot fine.
I swapped back in their original places R41's and R42's ends and...
black screen again.
I socketed and substituted another 3x4116 but that didn't revive the
PET. So I swapped again the CAS lines and I'm going to write some test
programs to understand what are the bits that don't work as expected.
Frank IZ8DWF


On Fri, Feb 3, 2017 at 1:35 PM, Francesco Messineo
<francesco.messineo@gmail.com> wrote:
> Hi all,
> I made no real progress on the 3032 so far. Using the pettester.bin
> image (is on zimmers.net) it seems that the RAM is good (I get a
> screen full of g's, alternating with the all characters screen). So
> the kernel ROM is addressed correctly.
> I could exclude the CPU (I have a spare one) and the ROMs. I
> substituted kernel and both basic ROM's sockets too, however I have
> continuity on all pins, so it wasn't strictly needed.
> 16 to 1 decoder looks as it's working, when the CPU enters a loop, I
> see it's cycling on most of the ROMs. Address buffers (LS244) looks
> good too, but I lack a logic analyzer to really have a good picture of
> what's going on :(
> Data path must be ok, otherwise there're few chances that the
> pettester.bin could work.
> The stock kernel gives a completely black screen most of the times (it
> clears the video ram, then gets stuck somewhere or enters a loop
> displaying a few characters).
> Next try will be swapping the ram bank's CAS lines as this problem is
> starting to smell like RAM addressing error or mirror (not detected by
> the simple pettester.bin).
> I'm tempted in writing a custom ROM to make tests easier, but maybe
> someone else already made debug ROMs for the PETs?
> Any hint is welcome anyway :)
>
> Frank  IZ8DWF

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