I do not believe there are any clearer schematics for the Horizons released into the wild. The ones for my 198+ model and the 3000 and 4000 models are pretty much what Bud released to the hands of those who chose to build their own. I built three of them using the included construction guide and they worked (at least the two I got complete,d before I stored everything away 20 years ago. Yep, just looking at them last night as I was going to try to find you something, till I found that Whtech had the same, brought back a lot of memories, good and bad). If the wires are not shown or talked about, maybe it was one of the various hacks for the Horizon, and I know nothing about those. Sorry if I didn't give you anything concrete to work with.
IT does say Horizon and date of 1986 also there is a stamp saying all mods ok '93. the Schematics on WTECH show 3 138s STACKED BUT they are not wired as this one was previously, ALSO when I did wire them as the schematic I could not even see the card and the LED would not light (data). BUT I went back to the original wiring of those 74LS138 stack and I am able to turn the card off \ on with >1000 using explorer. so im baffled, cause I use explorer and look into >4000 or so and all i see are Zeros. I plug in a number and it quickly erases and returns with zeros....somehow the card isn't firing up the ram? BUT im guessing the multiplexer is working??
Edited by GDMike, Wed Oct 24, 2018 3:33 PM.