There may well have been one of these. I've got a one or two of the ones a Denver company made for the Xerox 820 to insert a 1791/95 in place of the 1771. I even have the writeup somewhere, but no software patches. It just seems that I never have both the mezzanine board and the doc at the same time. Dick -----Original Message----- From: No Name <lsommo(a)hotmail.com> To: classiccmp(a)classiccmp.org <classiccmp(a)classiccmp.org> Date: Saturday, February 05, 2000 8:49 AM Subject: Re: What's a WD2793A chip? Wasn't there an add-on developed for the Xerox 820/ Big Board that used the 2793? As I recall it was a a simpler (and less expensive) circuit as compared to the other add-on being offered at the time. I had one and lost it (as well as my 256K memory expansion board) during the course of my moves. If anyone has the schematics for it I'd like to try and put another one together. Lou