Mike, Good info, thanks. I actually have a copy of the ON THREE manual...I forget where I found it or why I have it, because I wasn't aware that I had that board until a couple of days ago. Thanks for the offer of the loaner board. I may take you up on that, but let me try using the ON THREE manual and making sure the board is installed correctly and and everything is seated properly. And, if I can pinpoint the bad chips, I might try ordering some replacements to see if it can be fixed. If I eventually do swap in one of your loaner boards, I'm wondering if I can roll the other changes back? It looks like there were a number of mods made to the motherboard to accomodate the 512K board....including new ROMs. I certainly don't have the original ROMs to put back. At any rate, my holiday vacation time and the disproportionate amount of time I've been able to spend on this hobby, is about to end, so it may take me a bit of time to get to all of it. But thanks very much for all the info, I feel like I have a much clearer picture of how the III works and what I need to do. Win Hi Win, Yes, bad RAM could definitely cause that. The board you have was manufactured by ON THREE, which got its start as an Apple III users group. Once Apple turned its back on the III, ON THREE stepped up and began producing its own hardware and software for the computer. Apple had advertised the III as being expandable up to 512K, but never released a board larger than 256K. As the ON THREE engineers discovered, it required some new ROMs and additional addressing lines, but they got it working. That 512K board is fairly rare and sought after by III collectors, as SOS and big programs like Pascal can really benefit from the extra room. I'm not sure how easy it is to locate replacement chips for that board these days. Last time I checked (a few years ago), they were still available if you knew where to look. I have a few extra RAM boards for the III (256K and 128K, though - not 512K). I could loan you one for troubleshooting purposes, if you're interested. I wrote a quick blog entry a while back about ON THREE's card: http://www.6502lane.net/2011/01/17/a-look-at-on-threes-512k-memory-board-fo… Also, I have a PDF version of the user manual that came with it. The links in that blog entry are dead, but I can upload it, if you want. - Mike