Identifying bad RAM on Amiga 1000 WCS board

[Ethan Dicks]

On Mon, Apr 30, 2018 at 12:08 PM, Ethan Dicks <ethan.dicks at gmail.com> wrote:
> On Mon, Apr 30, 2018 at 11:24 AM, Peter Corlett via cctalk
> <cctalk at classiccmp.org> wrote:
>> On Mon, Apr 30, 2018 at 10:29:13AM -0400, Ethan Dicks via cctalk wrote:
>>> [...] The exact value to write to which address is documented somewhere....
>
>> As far as I can tell from the code, a 68000 RESET sets the latch such that
>> F80000-FBFFFF contains the boot ROM and FC0000-FFFFFF is the writable WCS.

Yep.  Confirmed with the Fluke.  You can write any value to $F000 000A
and the pod will reset the processor, which _does_ enable the WCS RAM
for writes.

>> A
>> *write* to F80000 (and probably any other address up to FBFFFF) flips the latch
>> such that the WCS is write-protected and is mirrored throughout the region
>> F80000-FFFFFF.

Confirmed with the real hardware.  A write to any address from $F80000
through $FBFFFE does flip the WCS write-protect latch and does mirror
WCS at $F80000

> I have a Fluke 9010A and will be soldering in the replacement RAM chip
> today

Replacement 41464 installed.  Fluke tests pass!  All the RAM is good!
The Amiga won't boot to Kickstart with the Fluke in place (there are
known effects of having the pod in place of a real CPU, including a
15ns delay on everything) but with the original CPU in the socket, it
boots right up to the Kickstart screen now.

-ethan