[vcf-midatlantic] Apple Branded Mid-80's Memory Compatibility Question.

[Ian Primus]

The later ROM revisions actually do have a reasonably competent memory
test you can access with control open-Apple solid-Apple reset, but the
first rev, ROM 255, doesn't. Also, if you haven't seen it yet, the
ROM4x project adds some neat stuff as well:
https://github.com/mgcaret/rom4x

If I'm working on a IIc and I'm at home and have access to my
equipment, I usually wind up burning a new ROM and upgrading it, and
then use that to find the bad RAM. Note that if you're going from a
255, the new ROM is bigger, so you'll have to change a couple
motherboard jumpers. It's a good idea to upgrade off of 255 if that's
what your machine has (Do a PRINT PEEK(64447) and see what version you
have, would be 255, 0, 3, or 4), since the later revs add Unidisk 3
1/2" support and fix some serial bugs that let it work reliably at
higher speeds.

-Ian

On Mon, Aug 9, 2021 at 8:18 AM Mike Willegal via vcf-midatlantic
<vcf-midatlantic at lists.vcfed.org> wrote:
>
> Ian,
>
> Thanks for confirming.   It sure doesn’t look like there is clearance for a socket.  I’ve also fixed a couple of Mac128ks with bad memory over the years, but those systems did a POST that made debugging significantly easier.  This failure was in auxiliary memory and I ended up modifying my 6502 memtest program to run from auxiliary memory in order to identify the bad chip.
>
> Mike Willegal