DTC01 DECtalk repaired

[Eric Smith]

Thanks to the source code for the MAME DTC01 DECtalk driver, which is
apparently the only place there is any information on the self-test
error LED codes, I determined that there was a failed HM6264LP-12
static RAM chip. The error code narrows it down to a pair, and
swapping narrowed it down to a single chip.  After replacement with an
HM6264ALP-12, and powering up, I was delighted to hear "DECtalk
version one point eight is running."

At some point if I get sixteen 27128 or 27C128 EPROMs, or maybe eight
27256 or 27C256 with four jumper changes on the board, and two 82S191
or equivalent PROMs, I might upgrade it to 2.0.

I've only ever seen firmware versions 1.8 and 2.0, but there are
rumors of an intermediate version and a version 2.1.  Does anyone have
these?