The D&N MEM-CM9 board combines 24K or RAM with a disk controller. The benefit is that it replaces both the OSI 527 and the OSI 470 board, leaving one extra slot free on the back plane.
I spent some time this going over the D&N MEM-CM9 board. I fixed some broken traces, cleaning up some oxidization on the connectors, replaced some missing and broken capacitors, dropping in a DIP switch (for memory addressing), and removing unwanted jumpers for 8" drive setup...and it works!!! Well, at least the one bank of memory that is populated (out of the three banks) works. I assigned the one bank of memory to the 4000-5FFF range, and was able to test it using the memory test program I previously typed in (that program has proved to be very useful), with no problems found.
I purchased a stack of 18pin sockets to populate the rest of the board. As there were a lot of sockets needed I actually opted for the cheaper non machined type, although of course I got dual site type. I also noticed that the board was missing a a 74LS138 which would be needed if I want to access the extra memory banks, so I purchased on of those too.
I looked through my parts box and found a small stack of twenty 2114 RAM and with this I was able to get the 8K bank up and running too. One thing that tripped me up was that the 74138, when using the 8k bank, needs a small jumper between pins 4 and 5. Pretty simple really.
I used up all my extra RAM, and with the 8k already on the 502 board I am now able to fill memory from 0000 to 6FFF. I also found a couple of duds chips in the process. I was only 8 chips short of a full set, so I purchased some extra from eBay.
PROJECTS AND ARTICLES
Repairing a D&N MEM-C9 board
After fixing broken traces and replacing missing capacitor, but before populating the board.
After populating the board with sockets and RAM. Still working.
Microsoft Basic reports a full complement of RAM available. This includes the extra 8K already on the 502 board for a total of 32K.
FInally the missing 2114 RAM arrived and I was able to populate the rest of the board and get the full 24K of RAM, both 16k and 8k, fully functional.
Of course I still have no idea if the disk section works as my drive is not working. Once I get a floppy system up and running I'll test to see if this board works for floppy access.