> The 2001 schematics... the ones with the 2316 ROMs. Every two of them > are connected to exactly the same lines, even select lines... Two 2316 ROMs do indeed have exactly the same lines. Theses ROMs are arranged in pairs in a 4K block. The 2316 ROMs have programmable select lines. One is programmed to respond in the lower 2K and the other is programmed to respond in the upper 2K. You can exchange the two ROMs in a pair and the machine will function as it did before. See my description of the system boards for which sockets are addressable in which address range. You can also remove both 2K ROMs in a pair and replace it with one 4K ROM in one of the sockets. For instance, if you have the 2316 Basic 2 ROMs in the 2001, you can remove both 2316s in a pair and use the equivalent 2332 ROM from the 2001N in their place. Also, you can program a 2532 EPROM with the contents of a 4K block and use it instead of the original 2K ROMs. In fact, this is the preferred method for replacements as it eliminates potential addressing conflists from 2516 EPROMs. > One more comment to the 2001N schematics. One might wonder why the ROM for > $E*** is selected with /SELE only... the IC (if and only if 2k) is > selected only when A11 is low, i.e. $E000-$E7FF. And you should better > not put a 4k ROM in there :-) It might seem that A11 should be handled differently in order to avoid potential problems, but there is a jumper that puts the I/O block at $8800(jumper R) instead of $E800(jumper S). This would allow a 4K ROM at $E000. I know of no machine that is configured that way, but the board allows for it. > There seems to be some anomaly on the 8032090-7.gif picture: in reality > jumpers 1,2,3,4 are not present, and they are not shown in the main > picture. However Detail A does show them. Jumpers 1 thru 4 are on sheet 6 of the schematics. J1 & J2 are at the top center. J3 & J4 are at the left near the 74LS393 at UD3. These select different clock timing for the 2K screen memory. > Also, while the pictures specify a 74415 in UE12, my 8032090 has a > "Mitsubishi M 53354 P 0870". So apparently they used different supplies > when convenient. You probably mean the 74154 at UE12. I cannot find any information on the M 53354. Commodore frequently used substitutes. Like any other company, they used whatever was cheapest. The part listed in the parts list should be considered as a specification. Any chip that meets the published specifications for the listed chip can be used.